Organic light emitting diode and organic light emitting device having the same

ABSTRACT

The present disclosure relates to an organic light emitting diode including an emitting material layer that has a host and two different delayed fluorescent materials whose energy levels are controlled and an organic light emitting device including the diode. Exciton energy is transferred from a first delayed fluorescent dopant to a second delayed fluorescent dopant, which has singlet and triplet energy levels lower than singlet and triplet energy levels of the first delayed fluorescent dopant and a narrow FWHM (full-width at half maximum) compared to the first delayed fluorescent dopant so that efficient light emission can be realized.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit under 35 U.S.C. § 119(a) ofKorean Patent Application No. 10-2018-0158906, filed in the Republic ofKorea on Dec. 11, 2018, which is incorporated herein by reference in itsentirety.

BACKGROUND Technical Field

The present disclosure relates to an organic light emitting diode, andmore specifically, to an organic light emitting diode having enhancedluminous efficiency and life span and an organic light emitting devicehaving the same.

Description of the Related Art

As display devices have become larger, there exists a need for a flatdisplay device with a lower space requirement. Among the flat displaydevices, a display device using an organic light emitting diode (OLED)has come into the spotlight.

In the OLED, when electrical charges are injected into an emission layerbetween an electron injection electrode (i.e., cathode) and a holeinjection electrode (i.e., anode), electrical charges are combined to bepaired, and then emit light as the combined electrical charges aredisappeared.

The OLED can be formed even on a flexible transparent substrate such asa plastic substrate. In addition, the OLED can be driven at a lowvoltage of 10 V or less. Besides, the OLED has relatively low powerconsumption for driving compared to plasma display panel and inorganicelectroluminescent devices, and its color purity is very high. Further,since the OLED can display various colors such as green, blue, red andthe likes, the OLED display device has attracted a lot of attention as anext-generation display device that can replace a liquid crystal displaydevice (LCD).

Since the blue luminous material should have very wide energy bandgapcompared to green or red luminous material, it has been difficult todevelop a blue luminous material. In addition, the organic lightemitting diode with a blue luminous material showed low luminousefficiency and an unsatisfactory life span and color purity.

BRIEF SUMMARY

Accordingly, the present disclosure is directed to an organic lightemitting diode and an organic light emitting device including theorganic light emitting diode that can reduce one or more of the problemsdue to the limitations and disadvantages of the related art.

An object of the present disclosure is to provide an organic lightemitting diode that can enhance its luminous efficiency and color purityand an organic light emitting device including the diode.

Another object of the present disclosure is to provide an organic lightemitting diode having an improved life span and an organic lightemitting device including the diode.

Additional features and advantages of the disclosure will be set forthin the description which follows, and in part will be apparent from thedescription, or may be learned by practice of the disclosure. Theobjectives and other advantages of the disclosure will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

According to an embodiment, the present disclosure provides an organiclight emitting diode that comprises first and second electrodes facingeach other; and an at least one emitting unit disposed between the firstand second electrodes and including an emitting material layer, whereinthe emitting material layer includes a host, a first delayed fluorescentdopant and a second delayed fluorescent dopant, wherein each of anexcited state singlet energy level (S₁ ^(TD1)) and an excited statetriplet energy level (T₁ ^(TD1)) of the first delayed fluorescent dopantis higher than each of an excited state singlet energy level (S₁ ^(TD1))and an excited state triplet energy level (T₁ ^(TD1)) of the seconddelayed fluorescent dopant, respectively, wherein a highest occupiedmolecular orbital (HOMO) energy level (HOMO^(H)) of the first host, aHOMO energy level (HOMO^(TD1)) of the first delayed fluorescent dopantand a HOMO energy level (HOMO^(TD2)) of the second delayed fluorescentdopant satisfy the following relationships in Equations (1) and (3), andwherein a lowest unoccupied molecular orbital (LUMO) energy level(LUMO^(H)) of the first host, a LUMO energy level (LUMO^(TD1)) of thefirst delayed fluorescent dopant and a LUMO energy level (LUMO^(TD2)) ofthe second delayed fluorescent dopant satisfy the followingrelationships in Equations (5) and (7).HOMO^(H)≤HOMO^(TD1)  (1)HOMO^(TD2)−HOMO^(TD1)>0.2 eV  (3)LUMO^(H)>LUMO^(TD1)  (5)LUMO^(TD1)≥LUMO^(TD2)  (7)

According to second embodiment, the present disclosure provides anorganic light emitting diode that comprises first and second electrodesfacing each other; and at least one emitting unit disposed between thefirst and second electrodes, wherein the at least one emitting unitcomprises an emitting material layer, wherein the emitting materiallayer includes a first emitting material layer disposed between thefirst and second electrodes, wherein the first emitting material layercomprises a first host and a first delayed fluorescent dopant, and asecond emitting material layer disposed between the first electrode andthe first emitting material layer or between the first emitting materiallayer and the second electrode, wherein the second emitting materiallayer comprises a second host and a second delayed fluorescent dopant,wherein each of an excited state singlet energy level (S₁ ^(TD1)) and anexcited state triplet energy level (T₁ ^(TD1)) of the first delayedfluorescent dopant is higher than each of an excited state singletenergy level (S₁ ^(TD1)) and an excited state triplet energy level (T₁^(TD2)) of the second delayed fluorescent dopant, respectively, whereina highest occupied molecular orbital (HOMO) energy level (HOMO^(H)) ofthe first host, a HOMO energy level (HOMO^(TD1)) of the first delayedfluorescent dopant and a HOMO energy level (HOMO^(TD2)) of the seconddelayed fluorescent dopant satisfy the relationships in Equations (1)and (3), and wherein a lowest unoccupied molecular orbital (LUMO) energylevel (LUMO^(H)) of the first host, a LUMO energy level (LUMO^(TD1)) ofthe first delayed fluorescent dopant and a LUMO energy level(LUMO^(TD2)) of the second delayed fluorescent dopant satisfy therelationships in Equations (5) and (7).

According to still another embodiment, the present disclosure providesan organic light emitting device that comprises a substrate and the OLEDdisposed over the substrate, as described above.

It is to be understood that both the foregoing general description andthe following detailed description are examples and are explanatory andare intended to provide further explanation of the disclosure asclaimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure, are incorporated in and constitute apart of this specification, illustrate implementations of the disclosureand together with the description serve to explain the principles ofembodiments of the disclosure.

FIG. 1 is a schematic cross-sectional view illustrating an organic lightemitting display device of the present disclosure.

FIG. 2 is a schematic cross-sectional view illustrating an organic lightemitting diode in accordance with an exemplary embodiment of the presentdisclosure.

FIG. 3 is a schematic diagram illustrating a luminous mechanism of adelayed fluorescent material.

FIG. 4 is a schematic diagram illustrating luminous mechanism in thecase of using a plurality of delayed fluorescent materials havingdifferent excited state triplet energy levels in accordance with anexemplary embodiment of the present disclosure.

FIG. 5 is a schematic diagram illustrating HOMO and LUMO energy levelrelationships among luminous materials in accordance with an exemplaryembodiment of the present disclosure.

FIG. 6 is a schematic diagram illustrating luminous mechanism by energylevel bandgap among luminous materials in accordance with an exemplaryembodiment of the present disclosure.

FIG. 7 is a schematic cross-sectional view illustrating an organic lightemitting diode in accordance with another exemplary embodiment of thepresent disclosure.

FIG. 8 is a schematic diagram illustrating luminous mechanism by energylevel bandgap among luminous materials in accordance with anotherexemplary embodiment of the present disclosure.

FIG. 9 is a schematic cross-sectional view illustrating an organic lightemitting diode in accordance with another exemplary embodiment of thepresent disclosure.

FIG. 10 is a schematic diagram illustrating luminous mechanism by energylevel bandgap among luminous materials in accordance with anotherexemplary embodiment of the present disclosure.

FIG. 11 is a schematic cross-section view illustrating an organic lightemitting diode in accordance with another exemplary embodiment of thepresent disclosure.

FIGS. 12 to 14 are graphs each of which illustrates an External QuantumEfficiency (EQE) as a function of current density changes in an organiclight emitting diode fabricated by applying a plurality of delayedfluorescent materials in accordance with Examples of the presentdisclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to aspects of the disclosure,examples of which are illustrated in the accompanying drawings.

[Organic Light Emitting Device]

An organic light emitting diode of the present disclosure includes aplurality of delayed fluorescent materials in an emitting material layerso as to enhance its luminous efficiency, its life span and its colorpurity. The organic light emitting diode of the present disclosure maybe applied to an organic light emitting device such as an organic lightemitting display device and an organic light emitting illuminationdevice. A display device including the organic light emitting diode willbe explained. FIG. 1 is a schematic cross-sectional view of an organiclight emitting display device of the present disclosure.

As illustrated in FIG. 1, the organic light emitting display device 100includes a substrate 102, a thin-film transistor Tr on the substrate102, and an organic light emitting diode 200 connected to the thin filmtransistor Tr.

The substrate 102 may include, but is not limited to, glass, thinflexible material and/or polymer plastics. For example, the flexiblematerial may be selected from the group, but is not limited to,polyimide (PI), polyethersulfone (PES), polyethylenenaphthalate (PEN),polyethylene terephthalate (PET), polycarbonate (PC) and combinationsthereof. The substrate 102, over which the thin film transistor Tr andthe organic light emitting diode 200 are arranged, form an arraysubstrate.

A buffer layer 104 may be disposed over the substrate 102, and the thinfilm transistor Tr is disposed over the buffer layer 104. The bufferlayer 104 may be omitted.

A semiconductor layer 110 is disposed over the buffer layer 104. In oneexemplary embodiment, the semiconductor layer 110 may include, but isnot limited to, oxide semiconductor materials. In this case, alight-shield pattern may be disposed under the semiconductor layer 110,and the light-shield pattern can prevent light from being incidenttoward the semiconductor layer 110, and thereby, preventing thesemiconductor layer 110 from being deteriorated by the light.Alternatively, the semiconductor layer 110 may include, but is notlimited to, polycrystalline silicon. In this case, opposite edges of thesemiconductor layer 110 may be doped with impurities.

A gate insulating layer 120 formed of an insulating material is disposedon the semiconductor layer 110. The gate insulating layer 120 mayinclude, but is not limited to, an inorganic insulating material such assilicon oxide (SiO_(x)) or silicon nitride (SiN_(x)).

A gate electrode 130 made of a conductive material such as a metal isdisposed over the gate insulating layer 120 so as to correspond to acenter of the semiconductor layer 110. While the gate insulating layer120 is disposed over a whole area of the substrate 102 in FIG. 1, thegate insulating layer 120 may be patterned in the same way as the gateelectrode 130.

An interlayer insulating layer 140 formed of an insulating material isdisposed on the gate electrode 130 so that it covers the entire surfaceof the substrate 102. The interlayer insulating layer 140 may include,but is not limited to, an inorganic insulating material such as siliconoxide (SiO_(x)) or silicon nitride (SiN_(x)), or an organic insulatingmaterial such as benzocyclobutene or photo-acryl.

The interlayer insulating layer 140 has first and second semiconductorlayer contact holes 142 and 144 that expose both sides of thesemiconductor layer 110. The first and second semiconductor layercontact holes 142 and 144 are disposed over opposite sides of the gateelectrode 130 and spaced apart from the gate electrode 130. The firstand second semiconductor layer contact holes 142 and 144 are formedwithin the gate insulating layer 120 in FIG. 1. Alternatively, the firstand second semiconductor layer contact holes 142 and 144 are formed onlywithin the interlayer insulating layer 140 when the gate insulatinglayer 120 is patterned in the same way as the gate electrode 130.

A source electrode 152 and a drain electrode 154, which are formed of aconductive material such as a metal, are disposed on the interlayerinsulating layer 140. The source electrode 152 and the drain electrode154 are spaced apart from each other with respect to the gate electrode130, and contact both sides of the semiconductor layer 110 through thefirst and second semiconductor layer contact holes 142 and 144,respectively.

The semiconductor layer 110, the gate electrode 130, the sourceelectrode 152 and the drain electrode 154 constitute the thin filmtransistor Tr, which acts as a driving element. The thin film transistorTr in FIG. 1 has a coplanar structure in which the gate electrode 130,the source electrode 152 and the drain electrode 154 are disposed overthe semiconductor layer 110. Alternatively, the thin film transistor Trmay have an inverted staggered structure in which a gate electrode isdisposed under a semiconductor layer and a source and a drain electrodeare disposed over the semiconductor layer. In this case, thesemiconductor layer may comprise amorphous silicon.

A gate line and a data line, which cross each other to define a pixelregion, and a switching element, which is connected to the gate line andthe data line, may be further formed in the pixel region in FIG. 1. Theswitching element is connected to the thin film transistor Tr, which isa driving element. Besides, a power line is spaced apart in parallelfrom the gate line or the data line, and the thin film transistor Tr mayfurther include a storage capacitor configured to constantly keep avoltage of the gate electrode for one frame.

In addition, the organic light emitting display device 100 may include acolor filter for absorbing a part of the light emitted from the organiclight emitting diode 200. For example, the color filter may absorb alight of specific wavelength such as red (R), green (G) or blue (B). Inthis case, the organic light emitting display device 100 can implementfull-color through the color filter.

For example, when the organic light emitting display device 100 is abottom-emission type, the color filter may be disposed on the interlayerinsulating layer 140 beneath the organic light emitting diode 200.Alternatively, when the organic light emitting display device 100 is atop-emission type, the color filter may be disposed above the organiclight emitting diode 200, that is, a second electrode 220.

A passivation layer 160 is disposed on the source and drain electrodes152 and 154 over the whole substrate 102. The passivation layer 160 hasa flat top surface and a drain contact hole 162 that exposes the drainelectrode 154 of the thin film transistor Tr. While the drain contacthole 162 is disposed on the second semiconductor layer contact hole 154,it may be spaced apart from the second semiconductor layer contact hole154.

The organic light emitting diode 200 includes a first electrode 210 thatis disposed on the passivation layer 160 and connected to the drainelectrode 154 of the thin film transistor Tr. The organic light emittingdiode 200 further includes an emitting unit 230 as an emission layer anda second electrode 220 each of which is disposed sequentially on thefirst electrode 210.

The first electrode 210 is disposed in each pixel region. The firstelectrode 210 may be an anode and include a conductive material having arelatively high work function value. For example, the first electrode210 may include, but is not limited to, a transparent conductivematerial such as indium tin oxide (ITO), indium zinc oxide (IZO), indiumtin zinc oxide (ITZO), tin oxide (SnO), zinc oxide (ZnO), indium ceriumoxide (ICO), aluminum doped zinc oxide (AZO), and the likes.

In one exemplary embodiment, when the organic light emitting displaydevice 100 is a top-emission type, a reflective electrode or areflective layer may be disposed under the first electrode 210. Forexample, the reflective electrode or the reflective layer may include,but is not limited to, aluminum-palladium-copper (APC) alloy.

In addition, a bank layer 170 is disposed on the passivation layer 160in order to cover edges of the first electrode 210. The bank layer 170exposes a center of the first electrode 210.

An emitting unit 230 is disposed on the first electrode 210. In oneexemplary embodiment, the emitting unit 230 may have a mono-layeredstructure of an emitting material layer. Alternatively, the emittingunit 230 may include a plurality of charge transfer layers in additionto an emitting material layer. As an example, the emitting unit 230 mayhave a multiple-layered structure of a hole injection layer, a holetransport layer, an electron blocking layer, an emitting material layer,a hole blocking layer, an electron transport layer and/or an electroninjection layer (See, FIGS. 2, 7, 9 and 11). In one embodiment, theorganic light emitting diode 200 may have one emitting unit 230.Alternatively, the organic light emitting diode 200 may have multipleemitting units 230 to form a tandem structure. The emitting materiallayer may include a host, a first delayed fluorescent dopant and asecond delayed fluorescent dopant.

The second electrode 220 is disposed over the substrate 102 above whichthe emitting unit 230 is disposed. The second electrode 220 may bedisposed over a whole display area and may include a conductive materialwith a relatively low work function value compared to the firstelectrode 210. The second electrode 220 may be a cathode. For example,the second electrode 220 may include, but is not limited to, aluminum(Al), magnesium (Mg), calcium (Ca), silver (Ag), alloys thereof orcombinations thereof such as aluminum-magnesium alloy (Al—Mg).

In addition, an encapsulation film 180 may be disposed over the secondelectrode 220 in order to prevent outer moisture from penetrating intothe organic light emitting diode 200. The encapsulation film 180 mayhave, but is not limited to, a laminated structure of a first inorganicinsulating film 182, an organic insulating film 184 and a secondinorganic insulating film 186.

[Organic Light Emitting Diode]

FIG. 2 is a schematic cross-sectional view illustrating an organic lightemitting diode in accordance with an exemplary embodiment of the presentdisclosure. As illustrated in FIG. 2, the organic light emitting diode(OLED) 300 in accordance with the first embodiment of the presentdisclosure includes first and second electrodes 310 and 320 facing eachother, an emitting unit 330 as an emission layer disposed between thefirst and second electrodes 310 and 320. In one exemplary embodiment,the emitting unit 330 include a hole injection layer HIL 340, a holetransport layer HTL 350, an emitting material layer EML 360, an electrontransport layer ETL 370 and an electron injection layer EIL 380 each ofwhich is laminated sequentially from the first electrode 310.Alternatively, the emitting unit 330 may further comprise a firstexciton blocking layer, i.e. an electron blocking layer (EBL) 355disposed between the HTL 350 and the EML 360 and/or a second excitonblocking layer, i.e. a hole blocking layer (HBL) 375 disposed betweenthe EML 360 and the ETL 370.

The first electrode 310 may be an anode that provides a hole into theEML 360. The first electrode 310 may include, but is not limited to, aconductive material having a relatively high work function value, forexample, a transparent conductive oxide (TCO). In an exemplaryembodiment, the first electrode 310 may include, but is not limited to,ITO, IZO, ITZO, SnO, ZnO, ICO, AZO, and the likes.

The second electrode 320 may be a cathode that provides an electron intothe EML 360. The second electrode 320 may include, but is not limitedto, a conductive material having a relatively low work function values,i.e., a highly reflective material such as Al, Mg, Ca, Ag, alloythereof, combinations thereof, and the likes.

The HIL 340 is disposed between the first electrode 310 and the HTL 350and improves an interface property between the inorganic first electrode310 and the organic HTL 350. In one exemplary embodiment, the HIL 340may include, but is not limited to,4,4′4″-Tris(3-methylphenylamino)triphenylamine (MTDATA),4,4′,4″-Tris(N,N-diphenyl-amino)triphenylamine (NATA),4,4′,4″-Tris(N-(naphthalene-1-yl)-N-phenyl-amino)triphenylamine(1T-NATA),4,4′,4″-Tris(N-(naphthalene-2-yl)-N-phenyl-amino)triphenylamine(2T-NATA), Copper phthalocyanine (CuPc),Tris(4-carbazoyl-9-yl-phenyl)amine (TCTA),N,N′-Diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4″-diamine (NPB;NPD), 1,4,5,8,9,11-Hexaazatriphenylenehexacarbonitrile(Dipyrazino[2,3-f:2′3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile;HAT-CN), 1,3,5-tris[4-(diphenylamino)phenyl]benzene (TDAPB),poly(3,4-ethylenedioxythiphene)polystyrene sulfonate (PEDOT/PSS) and/orN-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine.The HIL 340 may also be omitted according to one inventive embodiment ofthe OLED 300.

The HTL 350 is disposed adjacently to the EML 360 between the firstelectrode 310 and the EML 360. In one exemplary embodiment, the HTL 350may include, but is not limited to,N,N′-Diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD),NPB, 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP),Poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-benzidine] (Poly-TPD),Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine))](TFB), Di-[4-(N,N-di-p-tolyl-amino)-phenyl]cyclohexane (TAPC),N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amineand/orN-(biphenyl-4-yl)-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)biphenyl-4-amine.

The EML 360 may include a host doped with a plurality of delayedfluorescent materials. In an exemplary embodiment, the EML 360 may emitblue light, but is not limited thereto. As an example, the EML 360 mayinclude a host (first host; H), a first delayed fluorescent dopant (TD1)and a second delayed fluorescent dopant (TD2). When the EML 360 includesthe delayed fluorescent materials, it is possible to fabricate OLED 300with a further enhanced luminous efficiency.

Organic Light Emitting Diode (OLED) emits light as holes injected fromthe anode and electrons injected from the cathode are combined to formexcitons in EML and then unstable excited state excitons return to astable ground state. When electrons recombine with holes to formexciton, singlet excitons of a paired spin and triplet excitons of anunpaired spin are produced by a ratio of 1:3 by spin arrangements intheory. Within common fluorescent materials only the singlet excitonamong the excitons can be involved in emission process within the commonfluorescent materials. Accordingly, the OLED may exhibit luminousefficiency up to 5% when the common fluorescent material is used as aluminous material.

In contrast, phosphorescent materials use different luminous mechanismof converting singlet excitons as well as triplet excitons into light.Phosphorescent materials can convert singlet excitons into tripletexcitons through intersystem crossing (ISC). Since phosphorescentmaterials use both, singlet and triplet excitons during the luminousprocess, it is possible to enhance luminous efficiency when the OLEDuses phosphorescent materials as luminous materials compared tofluorescent materials. However, prior art blue phosphorescent materialsexhibit too low color purity to apply with the display device andexhibit very short luminous life span, and therefore, they have not beenused in commercial display devices.

Recently, a delayed fluorescent material, which can solve the problemsaccompanied by the prior art fluorescent and/or phosphorescentmaterials, has been developed. Representative delayed fluorescentmaterial is a thermally-activated delayed fluorescent (TADF) material.Since the delayed fluorescent material generally has both an electrondonor moiety and an electron acceptor moiety within its molecularstructure, it can be converted to an intramolecular charge transfer(ICT) state. In case of using the delayed fluorescent material as adopant, it is possible to use both the excitons of singlet energy levelS₁ and the excitons of triplet energy level T₁ during the emissionprocess.

The luminous mechanism of the delayed fluorescent material will beexplained with referring to FIG. 3, which is a schematic diagramillustrating a luminous mechanism of a delayed fluorescent material andillustrates a state of exciton energy loss by converting an excitedstate triplet exciton to a hot triplet exciton.

As illustrated in FIG. 3, the excitons of singlet energy level S₁ ^(TD)are emitted as fluorescence. On the contrary, the excitons of tripletenergy level T₁ ^(TD) are charge transfer (CT) state because the tripletexciton can be transferred to the ICT state. Since the exciton at CTstate can have singlet characteristics as well as tripletcharacteristics, the exciton at CT state in the delayed fluorescentmaterial can move to an exciton of singlet energy level by ReverseIntersystem Crossing (RISC) mechanism, and then the converted exciton ofsinglet energy level is transferred to a ground state (S₀ ^(TD); S₁^(TD)→ICT←T₁ ^(TD1)). Since the excitons of singlet energy level S₁^(TD1) as well as the excitons of triplet energy level T₁ ^(TD1) in thedelayed fluorescent material are involved in the emission process, thedelayed fluorescent material can improve its internal quantum efficiencyand its luminous efficiency.

Since both the Highest Occupied Molecular Orbital (HOMO) and the LowestUnoccupied Molecular orbital (LUMO) are widely distributed over thewhole molecule within the common fluorescent material, it is notpossible to inter-convert exciton energies between the singlet energylevel and the triplet energy level within the common fluorescentmaterial (selection rule). In contrast, since the delayed fluorescentmaterial, which can be converted to ICT state, has little orbitaloverlaps between HOMO and LUMO, there is little interaction between theHOMO state molecular orbital and the LUMO state molecular orbital. As aresult, the changes of spin states of electrons do not have an influenceon other electrons, and a new charge transfer band (CT band) that doesnot follow the selection rule is formed within the delayed fluorescentmaterial.

In other words, since the delayed fluorescent material has the electronacceptor moiety spacing apart from the electron donor moiety within themolecule, it exists as a polarized state having a large dipole momentwithin the molecule. As the interaction between HOMO molecular orbitaland LUMO molecular orbital becomes little in the state where the dipolemoment is polarized, the excitons at triplet energy level can beconverted to ICT state where the exciton becomes CT state in which theexcitons has triplet characteristics as well as singlet characteristics.As the triplet exciton at CT state is converted into singlet exciton byRISC, a delayed fluorescence occurs. Accordingly, the excitons oftriplet energy level T₁ ^(TD) as well as the excitons of singlet energylevel S₁ ^(TD) can be involved in the emission process.

In case of driving an organic light emitting diode that includes thedelayed fluorescent material, 25% excitons of singlet energy level S₁^(TD) and 75% excitons of triplet energy level T₁ ^(TD) are converted toICT state by heat or electrical field, and then the converted excitonstransfer to the ground state S₀ with luminescence. Therefore, thedelayed fluorescent material may have 100% internal quantum efficiencyin theory.

The delayed fluorescent material must has an energy level bandgapΔE_(ST) ^(TD) equal to or less than about 0.3 eV, for example, fromabout 0.05 to about 0.3 eV, between the singlet energy level S₁ ^(TD)and the triplet energy level T₁ ^(TD) so that exciton energy in both thesinglet energy level S₁ ^(TD) and the triplet energy level T₁ ^(TD) canbe transferred to the ICT state. The material having little energy levelbandgap between the singlet energy level S₁ ^(TD) and the triplet energylevel T₁ ^(TD) can exhibit common fluorescence by excitons of singletenergy level S₁ ^(TD), as well as delayed fluorescence with ReverseInter System Crossing (RISC) in which the excitons of triplet energylevel T₁ ^(TD) can be transferred upwardly to the excitons of singletenergy level S₁ ^(TD), and then the exciton of singlet energy level S₁^(TD) converted from the triplet energy level T₁ ^(TD) can betransferred to the ground state S₀ ^(TD).

However, additional charge transfer transition (CT transition) is causedin the delayed fluorescent material consisting of an electron donormoiety and an electron acceptor moiety owing to chemical conformationsand structural twists between those moieties. As a result, the delayedfluorescent material, including an electron donor moiety and an electronacceptor moiety, shows emission wavelength having very broad FWHM (fullwidth at half maximum) due to the luminescence property attributed tothe CT luminescence mechanism. Consequently, it has a limited potentialto be applied in a display device requiring high color purity.

In order to solve the limitation of the delayed fluorescent materialhaving a wide FWHM, it may be considered to apply a fluorescent materialhaving a relatively narrow FWHM. In this case, the triplet excitonenergy of the delayed fluorescent material is transferred to a tripletexciton of the fluorescent material with an up-conversion to the singletexciton of the delayed fluorescent material.

Due to the bond conformation between the electron acceptor and theelectron donor and sterical twists within the delayed fluorescentmaterial, as described above, additional charge transfer transitions (CTtransitions) are caused within the delayed fluorescent material. Sincethe delayed fluorescent material shows an emission spectrum having avery broad FWHM caused by the CT transition mechanism in the course ofthe emission, a poor color purity is obtained. That is, since thedelayed fluorescent material emits light by CT luminescence mechanismutilizing triplet exciton energy, it has a very short luminous life spanand a limit in terms of color purity caused by its wide FWHM.

A hyper-fluorescence accompanied by a delayed fluorescent materialsolves the limitations. It uses the delayed fluorescent material so asto raise a generation ratio of the singlet exciton in a fluorescentmaterial that can use only singlet exciton energy. Since the delayedfluorescent material can utilize the triplet exciton energy as well asthe singlet exciton energy, the fluorescent material can absorb theexciton energy released from the delayed fluorescent material, and thenthe exciton energy absorbed by the fluorescent material can be utilizedin the emission process with generating 100% singlet exciton.

However, since the triplet exciton of the fluorescent material does notparticipate in the luminescent mechanism, the triplet exciton energy ofthe delayed fluorescent material is quenched. Accordingly, the luminousefficiency of OLED further including the fluorescent material is reallyreduced by about 2 to 3% compared with the luminous efficiency of OLEDto which only the delayed fluorescent material is applied.

The EML 360 in the OLED 300 in accordance with the first embodimentincludes a plurality of delayed fluorescent materials whose energylevels are different from each other so that the OLED 300 can improveits luminous efficiency and color purity. FIG. 4 is a schematic diagramillustrating luminous mechanism in case of using a plurality of delayedfluorescent materials having different excited state triplet energylevels in accordance with an exemplary embodiment of the presentdisclosure.

As illustrated in FIGS. 2 and 4, the EML 360 includes a first delayedfluorescent dopant (TD1) and a second delayed fluorescent dopant (TD2)as a delayed fluorescent material. Each of an excited state singletenergy level S₁ ^(TD1) and an excited state triplet energy level T₁^(TD1) of the first delayed fluorescent dopant (TD1) is higher than eachof an excited state singlet energy level S₁ ^(TD2) and an excited statetriplet energy level T₁ ^(TD2) of the second delayed fluorescent dopant(TD2), respectively.

Accordingly, a part of an exciton energy at the excited state tripletenergy level T₁ ^(TD1) of the first delayed fluorescent dopant (TD1) isconverted to an exciton energy at the excited state singlet energy levelS₁ ^(TD1) by RISC mechanism (up-conversion), and the rest of an excitonenergy at the excited state triplet energy level of the first delayedfluorescent dopant is transferred to an excited state triplet energylevel T₁ ^(TD2) of the second delayed fluorescent dopant (TD2). Theexciton energy at the excited state singlet energy level S₁ ^(TD1),which is converted from the excited state triplet energy level T₁ ^(TD1)of the first delayed fluorescent dopant (TD1), is transferred to excitonenergy at the excited state singlet energy level S₁ ^(TD2) of the seconddelayed fluorescent dopant (TD2). The exciton energy at the excitedstate triplet energy level T₁ ^(TD2) of the second delayed fluorescentdopant (TD2), which is transferred from the excited state triplet energylevel T₁ ^(TD1) of the first delayed fluorescent dopant (TD1), isconverted to exciton energy at the excited state singlet energy level S₁^(TD2) of the second delayed fluorescent dopant (TD2) by another RISCmechanism.

The second delayed fluorescent dopant (TD2) can emit light utilizing i)the exciton energy transferred from the excited state singlet energylevel S₁ ^(TD1) of the first delayed fluorescent dopant as well as ii)exciton energy transferred from the excited state triplet energy levelT₁ ^(TD1) of the first delayed fluorescent dopant (TD1) through theexcited state triplet energy level T₁ ^(TD2) of the second delayedfluorescent dopant (TD2) at the excited state singlet energy level S₁^(TD2). The exciton energy transferred from the first delayedfluorescent dopant is not quenched, but is harvested by the seconddelayed fluorescent dopant to be involved in the final luminescence byapplying a plurality of delayed fluorescent materials whose energylevels are controlled within predetermined ranges in accordance with thefirst embodiment of the present disclosure. The OLED 300 can maximizeits luminous efficiency to realize a hyper-fluorescence. Since finalluminescence occurs at the second delayed fluorescent dopant, which mayhave narrow FWHM, it is possible to fabricate an OLED having an improvedcolor purity.

In order to realize a delayed fluorescence, each of the first and seconddelayed fluorescent dopants (TD1 and TD2) has a smaller energy levelbandgap between the excited state singlet energy levels S₁ ^(TD1) and S₁^(TD1) and the excited state triplet energy levels T₁ ^(TD1) and T₁^(TD)2 than a common fluorescent material. As an example, an energylevel bandgap ΔE_(ST) ^(TD1) between the excited state singlet energylevel S₁ ^(TD1) and the excited state triplet energy level T₁ ^(TD1) ofthe first delayed fluorescent dopant (TD1) may be equal to or less thanabout 0.3 eV, for example about 0.05 to about 0.3 eV. Also, an energylevel bandgap ΔE_(ST) ^(TD2) between the excited state singlet energylevel S₁ ^(TD2) and the excited state triplet energy level T₁ ^(TD2) ofthe second delayed fluorescent dopant (TD2) may be equal to or less thanabout 0.2 eV, for example about 0.05 to about 0.2 eV.

Moreover, when the EML 360 includes the luminous materials such as thefirst host, the first delayed fluorescent dopant and the second delayedfluorescent dopant, highest occupied molecular orbital (HOMO) energylevels and/or lowest unoccupied molecular orbital (LUMO) energy levelsamong those luminous materials are considered as another importantfactor or parameter to realize efficient luminescence in the EML 360.FIG. 5 is a schematic diagram illustrating HOMO and LUMO energy levelrelationships among luminous materials in accordance with an exemplaryembodiment of the present disclosure.

As illustrated schematically in FIG. 5, a HOMO energy level HOMO^(H) ofthe host in the EML 360 (See, FIG. 2) is equal to or deeper (lower) thana HOMO energy level HOMO^(TD1) of the first delayed fluorescent dopant.In other words, the HOMO energy level HOMO^(H) of the host and the HOMOenergy level HOMO^(TD1) of the first delayed fluorescent dopant shouldsatisfy the following relationship in Equation (1):HOMO^(H)≤HOMO^(TD1)  (1)

When an energy level bandgap between the HOMO energy level HOMO^(H) ofthe host and the HOMO energy level HOMO^(TD1) of the first delayedfluorescent dopant is too large, the hole exciton energy may not betransferred to the first delayed fluorescent dopant. In one exemplaryembodiment, the HOMO energy level bandgap |HOMO^(H)−HOMO^(TD1)| betweenthe HOMO energy level HOMO^(H) of the host and the HOMO energy levelHOMO^(TD1) of the first delayed fluorescent dopant satisfies thefollowing relationship in Equation (2):|HOMO^(H)−HOMO^(TD1)|<0.3 eV  (2)

In addition, the first delayed fluorescent dopant should not interferewith the luminescence mechanism of the second delayed fluorescentdopant. Therefore, the HOMO energy level HOMO^(TD1) of the first delayedfluorescent dopant is deeper than a HOMO energy level HOMO^(TD2) of thesecond delayed fluorescent dopant. As an example, the HOMO energy levelHOMO^(TD1) of the first delayed fluorescent dopant and the HOMO energylevel HOMO^(TD2) of the second delayed fluorescent dopant satisfy thefollowing relationship in Equation (3):HOMO^(TD2)−HOMO^(TD1)>0.2 eV  (3)

When the HOMO energy levels of the host, the first delayed fluorescentdopant and the second delayed fluorescent dopant satisfy therelationships in Equations (1) and (3), the holes injected into the hostcan be injected into the second delayed fluorescent dopant via the firstdelayed fluorescent dopant. Accordingly, the holes are recombined withelectrons at the second delayed fluorescent dopant irrespective of thefirst delayed fluorescent dopant so that light emission can occur at thesecond delayed fluorescent dopant.

As an example, when the HOMO energy level HOMO^(TD1) of the firstdelayed fluorescent dopant is equal to or shallower than the HOMO energylevel HOMO^(TD2) of the second delayed fluorescent dopant, the holesinjected via the host is trapped at the first delayed fluorescentdopant. Accordingly, an excited complex, i.e. exciplex is formed betweenthe first delayed fluorescent dopant trapping holes and the seconddelayed fluorescent dopant absorbing electron excitons, ultimate lightemission peak is shifted toward longer wavelength ranges, and luminouslife span of the delayed fluorescent dopants are reduced.

In another exemplary embodiment, the HOMO energy level HOMO^(TD1) of thefirst delayed fluorescent dopant and the HOMO energy level HOMO^(TD2) ofthe second delayed fluorescent dopant may satisfy the followingrelationship in Equation (4):0.2 eV<HOMO^(TD2)−HOMO^(TD1)<1.0 eV  (4)

When the HOMO energy levels HOMO^(TD1) and HOMO^(TD2) of the first andsecond delayed fluorescent dopants satisfy the relationship in Equation(4), holes injected from the host can be transferred to the seconddelayed fluorescent dopant rapidly without being trapped at the firstdelayed fluorescent dopant.

Moreover, a LUMO energy level LUMO^(H) of the host in the EML 360 isshallower than a LUMO energy level LUMO′ of the first delayedfluorescent dopant with respect to a zero point on the energy scale. Inother words, the LUMO energy level LUMO^(H) of the host and the LUMOenergy level LUMO′ of the first delayed fluorescent dopant satisfy thefollowing relationship in Equation (5):LUMO^(H)>LUMO^(TD1)  (5)

In addition, the first delayed fluorescent dopant should not interferewith the luminescence mechanism of the second delayed fluorescentdopant. Therefore, a LUMO energy level LUMO^(TD1) of the first delayedfluorescent dopant is equal to or shallower than the LUMO energy levelLUMO^(TD2) of the second delayed fluorescent dopant with respect to azero point on the energy scale. As an example, the LUMO energy levelLUMO^(TD1) of the first delayed fluorescent dopant and the LUMO energylevel LUMO^(TD2) of the second delayed fluorescent dopant satisfy thefollowing relationship in Equation (7):LUMO^(TD1)≥LUMO^(TD2)  (7)

When the LUMO energy levels of the host, the first and second delayedfluorescent dopants satisfy the relationships in Equations (5) and (7),electrons injected to the host can be injected into the second delayedfluorescent dopant via the first delayed fluorescent dopant.Accordingly, the electrons are recombined with holes at the seconddelayed fluorescent dopant irrespective of the first delayed fluorescentdopant so that light emission can occur at the second delayedfluorescent dopant.

When an energy level bandgap between the LUMO energy level LUMO^(H) ofthe host and the LUMO energy level LUMO^(TD1) of the first delayedfluorescent dopant is too large, the electron exciton energy may not betransferred to the first delayed fluorescent dopant. In one exemplaryembodiment, the LUMO energy level bandgap |LUMO^(H)−LUMO^(TD1)| betweenthe LUMO energy level LUMO^(H) of the host and the LUMO energy levelLUMO^(TD1) of the first delayed fluorescent dopant thus satisfies thefollowing relationship in Equation (6):0.3 eV<LUMO^(H)−LUMO^(TD1)<1.0 eV  (6)

When the LUMO energy levels LUMO^(TD1) of the first delayed fluorescentdopant is deeper than the LUMO energy level LUMO^(TD2) of the seconddelayed fluorescent dopant, the electrons injected via the host istrapped at the first delayed fluorescent dopant. Accordingly, as anexciplex is formed between the first delayed fluorescent dopant trappingelectrons and the second delayed fluorescent dopant absorbing holeexcitons, ultimate light emission peak is shifted toward longerwavelength ranges, and luminous life span of the delayed fluorescentdopants are reduced.

In still another exemplary embodiment, the LUMO energy level LUMO^(TD1)of the first delayed fluorescent dopant and the LUMO energy levelLUMO^(TD2) of the second delayed fluorescent dopant may satisfy thefollowing relationship in Equation (8):|LUMO^(TD1)−LUMO^(TD2)|<0.2 eV  (8)

When the LUMO energy levels LUMO^(TD1) and LUMO^(TD2) of the first andsecond delayed fluorescent dopants satisfy the relationship in Equation(8), electrons injected from the host can be transferred to the seconddelayed fluorescent dopant rapidly without being trapped at the firstdelayed fluorescent dopant.

In one exemplary embodiment, the first delayed fluorescent dopant (TD1)may have a molecular structure in which an electron acceptor moiety andan electron donor moiety are connected via a proper linker so as torealize a delayed fluorescence. As an example, the first delayedfluorescent dopant (TD1) may include, but is not limited to, an organiccompound having the following structure of Chemical Formula 1:

-   -   In Chemical Formula 1, each of R₁ and R₂ is independently a        C₅˜C₃₀ aryl group or a C₄˜C₃₀ hetero aryl group. R₃ is halogen,        a C₁˜C₂₀ alkyl halide, a cyano group, a nitro group, a linear or        branched C₁˜C₂₀ alkyl group, a C₁˜C₂₀ alkoxy group, a C₅˜C₃₀        aryl group unsubstituted or substituted with a group selected        from halogen, a C₁˜C₂₀ alkyl halide, a cyano group, a nitro        group and combinations thereof, or a C₄˜C₃₀ hetero aryl group        unsubstituted or substituted with a group selected from halogen,        a C₁˜C₂₀ alkyl halide, a cyano group, a nitro group and        combinations thereof m is a number of substituent and is an        integer of 1 to 5. Ar₁ is a C₁₀˜C₃₀ fused hetero aryl group. L        is a C₅˜C₃₀ arylene group unsubstituted or substituted with one        or more groups selected from halogen, a C₁˜C₂₀ alkyl halide, a        cyano group, a nitro group and combinations thereof, or a C₄˜C₃₀        hetero arylene group unsubstituted or substituted with one or        more groups selected from halogen, a C₁˜C₂₀ alkyl halide, a        cyano group, a nitro group and combinations thereof.

As used herein, the term “unsubstituted” means that hydrogen atom isbonded, and in this case hydrogen atom comprises protium, deuterium andtritium.

As used herein, the term “hetero” described in “hetero aromatic ring”,“hetero aromatic group”, “hetero alicyclic ring”, “hetero cyclic alkylgroup”, “hetero aryl group”, “hetero aralkyl group”, “hetero aryloxylgroup”, “hetero aryl amino group”, “hetero arylene group”, “heteroaralkylene group”, “hetero aryloxylene group”, and the likes means thatat least one carbon atoms, for example 1 to 5 carbon atoms, forming sucharomatic or alicyclic rings are substituted with at least one heteroatoms selected from the group consisting of N, O, S and combinationsthereof.

As an example, each of the C₅˜C₃₀ aryl group constituting each of R₁ toR₃ may be independently, but is not limited to, a unfused or fused arylgroup such as phenyl, biphenyl, naphthyl, anthracenyl, indenyl,indacenyl, phenalenyl, phenanthrenyl, benzophenanthrenyl,dibenzophenanthrenyl, azulenyl, pyrenyl, fluoranthenyl, chrysenyl,tetraphenyl, tetracenyl, pleiadenyl, pycenyl, pentaphenyl, pentacenyl,fluorenyl, indenoindenyl, indenofluorenyl or spiro fluorenyl.

In another exemplary embodiment, each of the C₄˜C₃₀ hetero aryl groupconstituting each of R₁ to R₃ may be independently, an unfused or fusedhetero aryl group such as furanyl, thiophenyl, pyrrolyl, pyridinyl,pyrimidinyl, pyrazinyl, pyridazinyl, triazinyl, tetrazinyl, imidazolyl,pyrazolyl, indolyl, carbazolyl, benzocarbazolyl, dibenzocarbazolyl,indolocarbazolyl, indenocarbazolyl, benzofuranocarbazolyl,benzothienocarbazolyl, quinolinyl, iso-quinolinyl, phthalazinyl,quinoxalinyl, cinnolinyl, quinazolinyl, benzoquinolinyl,benzoiso-quinolinyl, benzoquinazolinyl, benzoquinoxalinyl, acridinyl,phenanthrolinyl, phenazinlyl, phenoxazinyl, phenothiazinyl, pyranyl,oxazinyl, oxazolyl, iso-oxazolyl, oxadiazolyl, triazolyl, dioxinyl,benzofuranyl, dibenzofuranyl, thiopyranyl, thiazinyl, benzothiophenyl,dibenzothiophenyl, spiro acridinyl linked to xanthene and the likes,dihydroacridnyl substituted with at least one C₁˜C₁₀ alkyl,N-substituted spiro fluorenyl (in case R₁ and R₂ are combined).

As an example, Ar₁, which is the electron donor moiety in ChemicalFormula 1, includes, but is not limited to, carbazolyl,indolocarbazolyl, phenazinly, phenoxazinyl, phenothiazinyl, acridinyl,spirofluoro acridinyl, spiroxantheno acridinyl and the likes.

In addition, L, which is a linker connecting the electron donor moietyAr₁ and the electron acceptor moiety triazine moiety, may be selectedfrom the group, but is not limited to, phenylene, biphenylene,terphenylene, tetraphenylene, indenylene, naphthylene, azulenylene,indacenylene, acenaphthylene, fluorenylene, spiro-fluorenylene,phenalenylene, phenanthrenylene, anthracenylene, fluoranthenylene,triphenylenylene, pyrenylene, chrysenylene, naphthacenylene, picenylene,perylenylene, pentaphenylene and hexacenylene.

In one exemplary embodiment, Ar₁ in Chemical Formula 1 may include acarbazolyl moiety. As an example, the first delayed fluorescent dopantmay include, but is not limited to, an organic compound having thefollowing structure of Chemical Formula 2:

In Chemical Formula 2, each of R₁₁ and R₁₂ is independently a C₅˜C₂₀aryl group. Each of R₁₃ to R₂₀ is independently protium, deuterium,tritium, a cyano group, a linear or branched C₁˜C₁₀ alkyl group, aC₅˜C₃₀ aryl amino group unsubstituted or substituted with C₅˜C₂₀ arylgroup, a C₅˜C₃₀ aryl group unsubstituted or substituted with a cyanogroup, or a C₄˜C₃₀ hetero aryl group unsubstituted or substituted with acyano group.

As an example, at least one of R₁₃ to R₂₀ in Chemical Formula 2 may notbe hydrogen.

Particularly, the first delayed fluorescent dopant may include, but isnot limited to, any of the following structures of Chemical Formula 3.

In another exemplary embodiment, the second delayed fluorescent dopantmay be an organic compound having a plurality of fused hetero aromaticmoieties and a narrow FWHM, unlike the first delayed fluorescent dopanthaving the electron donor moiety and the electron acceptor moiety. As anexample, the second delayed fluorescent dopant may include, but is notlimited to, an organic compound having the following structure ofChemical Formula 4:

In Chemical Formula 4, each of R₃₁ and R₃₂ is independently a linear orbranched C₁˜C₂₀ alkyl group, a C₁˜C₂₀ alkoxy group, a C₅˜C₃₀ aryl group,a C₄˜C₃₀ hetero aryl group or an aromatic or hetero aromatic aminogroup, wherein the amino group is substituted with a group selected fromthe group consisting of a C₅˜C₃₀ aryl group, a C₄˜C₃₀ hetero aryl group,a C₅˜C₃₀ aryl amino group unsubstituted or substituted with a C₅˜C₂₀aryl group, a C₄˜C₃₀ hetero aryl amino group unsubstituted orsubstituted with a C₄˜C₂₀ hetero aryl group and combinations thereof.Alternatively, two adjacent groups among each of R₃₁ and R₃₂ formrespectively a C₅˜C₂₀ fused aromatic ring or a C₄˜C₂₀ fused heteroaromatic ring. Wherein each of the C₅˜C₂₀ fused aromatic ring and theC₄˜C₂₀ fused hetero aromatic ring is independently unsubstituted orsubstituted with a C₅˜C₂₀ aryl group or a C₄˜C₂₀ hetero aryl group. Eachof o and p is a number of a substituent and an integer of 0 to 3. Eachof R₃₃ and R₃₄ is independently protium, deuterium, tritium, a linear orbranched C₁˜C₂₀ alkyl group, a C₁˜C₂₀ alkoxy group, a C₅˜C₃₀ aryl groupor a C₄˜C₃₀ hetero aryl group. R₃₅ is protium, deuterium, tritium, alinear or branched C₁˜C₂₀ alkyl group, a C₁˜C₂₀ alkoxy group or anaromatic or hetero aromatic amino group. Wherein the amino group issubstituted with a group selected from the group consisting of a C₅˜C₃₀aryl group, a C₄˜C₃₀ hetero aryl group and combinations thereof.

In accordance with an exemplary embodiment, each of the aryl group andthe hetero aryl group constituting each of R₃₁ to R₃₅ in ChemicalFormula 4 may be the same as the aryl group and the hetero aryl groupconstituting each of R₁ to R₃ in Chemical Formula 1. As an example, thesecond dopant may include, but is not limited to, an organic compoundhaving the following structure of Chemical Formula 5:

-   -   In Chemical Formula 5, each of R_(41a), R_(41b), R_(42a) and        R_(42b) is independently protium, deuterium, tritium, a linear        or branched C₁˜C₁₀ alkyl group, a C₅˜C₃₀ aryl group, a C₄˜C₃₀        hetero aryl group or an aromatic or hetero aromatic amino group,        wherein the amino group is substituted with a group selected        from the group consisting of a C₅˜C₃₀ aryl group, a C₄˜C₃₀        hetero aryl group, a C₅˜C₃₀ aryl amino group unsubstituted or        substituted with a C₅˜C₂₀ aryl group, a C₄˜C₃₀ hetero aryl amino        group unsubstituted or substituted with a C₄˜C₂₀ hetero aryl        group and combinations thereof. Alternatively, two adjacent        groups among R_(41a), R_(41b), R_(42a) and R_(42b) form        respectively a C₄˜C₂₀ fused hetero aryl ring unsubstituted or        substituted with a C₅˜C₂₀ aryl group. Each of R₄₃ and R₄₄ is        independently protium, deuterium, tritium, a linear or branched        C₁˜C₁₀ alkyl group or an aromatic or hetero aromatic amino        group. The amino group may be substituted with a group selected        from the group consisting of a C₅˜C₃₀ aryl group, a C₄˜C₃₀        hetero aryl group and combinations thereof. R₄₅ is protium,        deuterium tritium, a linear or branched C₁˜C₂₀ alkyl group, a        C₁˜C₂₀ alkoxy group or an aromatic or hetero aromatic amino        group, wherein the amino group is substituted with a group        selected from the group consisting of C₅˜C₃₀ aryl group, C₄˜C₃₀        hetero aryl group and combinations thereof.

Particularly, the second delayed fluorescent dopant may include, but isnot limited to, any having the following structures of Chemical Formula6.

When the EML 360 of the OLED 300 in accordance with the first embodimentof the present disclosure includes the host, the first and seconddelayed fluorescent dopants, the relationships of the singlet andtriplet energy levels among those luminous materials are explained withreferring to FIG. 6.

FIG. 6 is a schematic diagram illustrating luminous mechanism by energylevel bandgap among luminous materials in accordance with an exemplaryembodiment of the present disclosure. As illustrated in FIG. 6, theexciton energy generated at the host should be transferred to the seconddelayed fluorescent dopant via the first delayed fluorescent dopant inorder to emit light at the second delayed fluorescent dopant. Therefore,each of an excited state singlet energy level S₁ ^(H) and an excitedstate triplet energy level T₁ ^(H) of the host is higher than each ofexcited state singlet energy levels S₁ ^(TD1) and S₁ ^(TD2) and theexcited triplet energy levels T₁ ^(TD1) and T₁ ^(TD2) of the first andsecond delayed fluorescent dopants.

As an example, when the excited state triplet energy level T₁ ^(H) ofthe host is not higher than the excited state triplet energy level T₁^(TD1) of the first delayed fluorescent dopant, the triplet excitonenergy of the first delayed fluorescent dopant may be reverselytransferred to the excited state triplet energy level T₁ ^(H) of thehost. In this case, the triplet exciton is quenched non-radiatively atthe host where the triplet exciton cannot be emitted so that the tripletexciton energy of the first delayed fluorescent dopant cannot contributeto light emission. As an example, the excited state triplet energy levelT₁ ^(H) of the host may be higher than the excited state triplet energylevel T₁ ^(TD1) of the first delayed fluorescent dopant by at leastabout 0.2 eV.

The host is not limited to specific materials. It is only important thatthe excited state triplet energy level T₁ ^(H) is higher than theexcited state triplet energy levels T₁ ^(TD1) and T₁ ^(TD2) of thedelayed fluorescent dopants and its HOMO and LUMO energy levels HOMO^(H)and LUMO^(H) satisfy the relationships in Equations (1), (2), (5) and(6) compared to the HOMO and LUMO energy levels HOMO^(TD1), HOMO^(TD2),LUMO^(TD1) and LUMO^(TD2) of the delayed fluorescent dopants. As anexample, the first host may include, but is not limited to,9-(3-(9H-carbazol-9-yl)phenyl)-9H-carbazole-3-carbonitrile (mCP-CN),CBP, 3,3′-bis(N-carbazolyl)-1,1′-biphenyl (mCBP),1,3-Bis(carbazol-9-yl)benzene (mCP),Oxybis(2,1-phenylene))bis(diphenylphosphine oxide (DPEPO),2,8-bis(diphenylphosphoryl)dibenzothiophene (PPT),1,3,5-Tri[(3-pyridyl)-phen-3-yl]benzene (TmPyPB),2,6-Di(9H-carbazol-9-yl)pyridine (PYD-2Cz),2,8-di(9H-carbazol-9-yl)dibenzothiophene(DCzDBT),3′,5′-Di(carbazol-9-yl)-[1,1′-biphenyl]-3,5-dicarbonitrile(DCzTPA),4′-(9H-carbazol-9-yl)biphenyl-3,5-dicarbonitrile(4′-(9H-carbazol-9-yl)biphenyl-3,5-dicarbonitrile(pCzB-2CN), 3′-(9H-carbazol-9-yl)biphenyl-3,5-dicarbonitrile (mCzB-2CN),Diphenyl-4-triphenylsilylphenyl-phosphine oxide (TPSO1),9-(9-phenyl-9H-carbazol-6-yl)-9H-carbazole (CCP),4-(3-(triphenylen-2-yl)phenyl)dibenzo[b,d]thiophene),9-(4-(9H-carbazol-9-yl)phenyl)-9H-3,9′-bicarbazole,9-(3-(9H-carbazol-9-yl)phenyl)-9H-3,9′-bicarbazole and/or9-(6-(9H-carbazol-9-yl)pyridin-3-yl)-9H-3,9′-bicarbazole.

When the EML 360 includes the first and second delayed fluorescentdopants, the content of the second delayed fluorescent dopant is lessthan the content of the first delayed fluorescent dopant. When thecontent of the second delayed fluorescent dopant is more than thecontent of the first delayed fluorescent dopant, exciton energies maynot be transferred efficiently form the first delayed fluorescent dopantto the second delayed fluorescent dopant. As an example, the EML 360 mayinclude, but is not limited to, the host of about 50 to about 75% byweight, and preferably about 60 to about 75% by weight, the firstdelayed fluorescent dopant of about 20 to about 40% by weight and thesecond delayed fluorescent dopant of about 1 to about 10% by weight, andpreferably about 1 to about 5% by weight.

Referring to FIG. 2, the ETL 370 and the EIL 380 may be laminatedsequentially between the EML 360 and the second electrode 320. The ETL370 includes a material having a high electron mobility so as to stablyprovide electrons for the EML 360 by fast electron transportation.

In one exemplary embodiment, the ETL 370 may include, but is not limitedto, oxadiazole-based compounds, triazole-based compounds,phenanthroline-based compounds, benzoxazole-based compounds,benzothiazole-based compounds, benzimidazole-based compounds,triazine-based compounds, and the likes.

As an example, the ETL 370 may include, but is not limited to,tris-(8-hydroxyquinoline aluminum (Alq₃),2-biphenyl-4-yl-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD), spiro-PBD,lithium quinolate (Liq), 1,3,5-Tris(N-phenylbenzimidazol-2-yl)benzene(TPBi),Bis(2-methyl-8-quinolinolato-N1,O8)-(1,1′-biphenyl-4-olato)aluminum(BAlq), 4,7-diphenyl-1,10-phenanthroline (Bphen),2,9-Bis(naphthalene-2-yl)4,7-diphenyl-1,10-phenanthroline (NBphen),2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP),3-(4-Biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole (TAZ),4-(Naphthalen-1-yl)-3,5-diphenyl-4H-1,2,4-triazole (NTAZ),1,3,5-Tri(p-pyrid-3-yl-phenyl)benzene (TpPyPB),2,4,6-Tris(3′-(pyridin-3-yl)biphenyl-3-yl)1,3,5-triazine (TmPPPyTz),Poly[9,9-bis(3′-(N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene]-alt-2,7-(9,9-dioctylfluorene)](PFNBr) and/or tris(phenylquinoxaline) (TPQ).

The EIL 380 is disposed between the second electrode 320 and the ETL370, and can improve physical properties of the second electrode 320 andtherefore, can enhance the life span of the OLED 300. In one exemplaryembodiment, the EIL 380 may include, but is not limited to, an alkalihalide such as LiF, CsF, NaF, BaF₂ and the likes, and/or an organicmetal compound such as lithium quinolate, lithium benzoate, sodiumstearate, and the likes.

When holes are transferred to the second electrode 320 via the EML 360and/or electrons are transferred to the first electrode 310 via the EML360, the OLED 300 may have a short life span and a reduced luminousefficiency. In order to prevent these phenomena, the OLED 300 inaccordance with this embodiment of the present disclosure has at leastone exciton blocking layer adjacent to the EML 360.

For example, the OLED 300 of the exemplary embodiment includes the EBL355 between the HTL 350 and the EML 360 so as to control and preventelectron transfers. In one exemplary embodiment, the EBL 355 mayinclude, but is not limited to, TCTA, Tris[4-(diethylamino)phenyl]amine,N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluorene-2-amine,TAPC, MTDATA, mCP, mCBP, CuPc,N,N′-bis[4-(bis(3-methylphenyl)amino)phenyl]-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(DNTPD), TDAPB and/or 3,6-bis(N-carbazolyl)-N-phenyl-carbazole.

In addition, the OLED 300 further includes the HBL 375 as a secondexciton blocking layer between the EML 360 and the ETL 370 so that holescannot be transferred from the EML 360 to the ETL 370. In one exemplaryembodiment, the HBL 375 may include, but is not limited to,oxadiazole-based compounds, triazole-based compounds,phenanthroline-based compounds, benzoxazole-based compounds,benzothiazole-based compounds, benzimidazole-based compounds, andtriazine-based compounds.

For example, the HBL 375 may include a compound having a relatively lowHOMO energy level compared to the emitting material in EML 360. The HBL375 may include, but is not limited to, BCP, BAlq, Alq₃, PBD, spiro-PBD,Liq, Bis-4,5-(3,5-di-3-pyridylphenyl)-2-methylpyrimidine (B3PYMPM),DPEPO, 9-(6-(9H-carbazol-9-yl)pyridine-3-yl)-9H-3,9′-bicarbazole andcombinations thereof.

In accordance with an exemplary embodiment, the EML 360 includes asecond delayed fluorescent dopant having narrow FWHM so as to preventthat the color purity is deteriorated when only the first delayedfluorescent dopant is used. The triplet exciton energy of the firstdelayed fluorescent dopant is converted to singlet exciton energy of itsown by RISC mechanism, then the converted singlet exciton energy of thefirst delayed fluorescent dopant can be transferred to the seconddelayed fluorescent dopant within the same EML 360 by a Dexter energytransfer mechanism, which transfers exciton energies depending upon wavefunction overlaps among adjacent molecules by inter-molecular electronexchanges and exciton diffusions. As the exciton energy is transferredfrom the first delayed fluorescent dopant to the second delayedfluorescent dopant, ultimate light emission occurs as transferredexciton energy at the second delayed fluorescent dopant having narrowFWHM is shifted to the ground state. Accordingly, the luminousefficiency and life span of the OLED can be enhanced and its colorpurity can be improved.

In the above first embodiment, the OLED 300 includes a single-layeredEML 360. Alternatively, an OLED in accordance with the presentdisclosure may include a multiple-layered EML. FIG. 7 is a schematiccross-sectional view illustrating an organic light emitting diode inaccordance with another exemplary embodiment of the present disclosure.

As illustrated in FIG. 7, the OLED 400 in accordance with an exemplarythird embodiment of the present disclosure includes first and secondelectrodes 410 and 420 facing each other and an emitting unit 430 as anemission layer disposed between the first and second electrodes 410 and420.

In one exemplary embodiment, the emitting unit 430 includes an HIL 440,an HTL 450, and EML 460, an ETL 470 and an EIL 480 each of which islaminated sequentially over the first electrode 410. Besides, theemitting unit 430 may further include an EBL 455 as a first excitonblocking layer disposed between the HTL 450 and the EML 460, and/or anHBL 475 as a second exciton blocking layer disposed between the EML 460and the ETL 470.

As described above, the first electrode 410 may be an anode and mayinclude, but is not limited to, a conductive material having arelatively large work function values such as ITO, IZO, SnO, ZnO, ICO,AZO, and the likes. The second electrode 420 may be a cathode and mayinclude, but is not limited to, a conductive material having arelatively small work function values such as Al, Mg, Ca, Ag, alloythereof or combinations thereof.

The HIL 440 is disposed between the first electrode 410 and the HTL 450.The HIL 440 may include, but is not limited to, MTDATA, NATA, 1T-NATA,2T-NATA, CuPc, TCTA, NPB(NPD), HAT-CN, TDAPB, PEDOT/PSS and/orN-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine.The HIL 440 may be omitted in compliance with the structure of the OLED400.

The HTL 450 is disposed adjacently to the EML 460 between the firstelectrode 410 and the EML 460. The HTL 450 may include, but is notlimited to, aromatic amine compounds such as TPD, NPD(NPB), CBP,poly-TPD, TFB, TAPC,N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amineand/orN-(biphenyl-4-yl)-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)biphenyl-4-amine.

The EBL 455 may include, but is not limited to, TCTA,Tris[4-(diethylamino)phenyl]amine,N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluorene-2-amine,TAPC, MTDATA, mCP, mCBP, CuPc, DNTPD, TDAPB and/or3,6-bis(N-carbazolyl)-N-phenyl-carbazole.

The EML 460 includes a first EML (EML1) 462 and a second EML (EML2) 464.The EML1 462 is disposed between the EBL 455 and the HBL 475 and theEML2 464 is disposed between the EML1 462 and the HBL 475. Theconfiguration and energy levels among the luminous materials in the EML460 will be explained in more detail below.

The HBL 475 may include, but is not limited to, oxadiazole-basedcompounds, triazole-based compounds, phenanthroline-based compounds,benzoxazole-based compounds, benzothiazole-based compounds,benzimidazole-based compounds, and triazine-based compounds. As anexample, the HBL 475 may include a compound having a relatively low HOMOenergy level compared to the emitting material in EML 460. The HBL 475may include, but is not limited to, BCP, BAlq, Alq₃, PBD, spiro-PBD,Liq, B3PYMPM, DPEPO,9-(6-(9H-carbazol-9-yl)pyridine-3-yl)-9H-3,9′-bicarbazole andcombinations thereof.

The ETL 470 is disposed between the EML 460 and the EIL 480. In oneexemplary embodiment, the ETL 470 may include, but is not limited to,oxadiazole-based compounds, triazole-based compounds,phenanthroline-based compounds, benzoxazole-based compounds,benzothiazole-based compounds, benzimidazole-based compounds,triazine-based compounds, and the likes. As an example, the ETL 470 mayinclude, but is not limited to, Alq₃, PBD, spiro-PBD, Liq, TPBi, BAlq,Bphen, NBphen, BCP, TAZ, NTAZ, TpPyPB, TmPPPyTz, PFNBr and/or TPQ.

The EIL 480 is disposed between the second electrode 420 and the ETL470. In one exemplary embodiment, the EIL 480 may include, but is notlimited to, an alkali halide such as LiF, CsF, NaF, BaF₂ and the likes,and/or an organic metal compound such as lithium benzoate, sodiumstearate, and the likes.

As described above, the EML 460 includes the EML1 462 and the EML2 464.One of the EML1 462 and the EML2 464 includes a first host and the firstdelayed fluorescent dopant, and the other of the EML1 462 and the EML2464 includes a second host and a second delayed fluorescent dopant.Hereinafter, the EML 460, where the EML1 462 includes the first delayedfluorescent dopant and the EML2 464 includes the second delayedfluorescent dopant, will be explained.

In accordance with an exemplary second embodiment, the EML1 462 includesthe first host and the first delayed fluorescent dopants, and the EML2464 includes the second host and the second delayed fluorescent dopant.As described in the first embodiment, two delayed fluorescent materialshaving different triplet energy levels, HOMO energy levels and LUMOenergy levels can be applied into an EML to improve its luminousefficiency and its luminescence lifetime. Particularly, it is possibleto improve color purity by applying the second delayed fluorescentdopant having narrow FWHM into the EML 460.

In this exemplary second embodiment, the singlet exciton energy and thetriplet exciton energy of the first delayed fluorescent dopant in EML1462 can be transferred to the second delayed fluorescent dopant in theEML2 464 disposed adjacently to the EML1 462 by FRET (Forster resonanceenergy transfer) mechanism, which transfers energy non-radiativelythrough electrical fields by dipole-dipole interactions. Accordingly,the ultimate emission occurs in the second delayed fluorescent dopantwithin the EML2 464.

In other words, the triplet exciton energy of the first delayedfluorescent dopant is converted to the singlet exciton energy of its ownin the EML1 462 by the RISC mechanism (T₁ ^(TD1)→S₁ ^(TD1)), then theconverted singlet exciton energy of the first delayed fluorescent dopantis transferred to the singlet exciton energy of the second delayedfluorescent dopant in the EML2 464 because the excited state singletenergy level S₁ ^(TD1) of the first delayed fluorescent dopant in theEML1 462 is higher than the excited state singlet energy level S₁ ^(TD2)of the second delayed fluorescent dopant in the EML2 464 (See, FIG. 8).

The second delayed fluorescent dopant in the EML2 464 can emit lightusing the triplet exciton energy as well as the singlet exciton energyof the first delayed fluorescent dopant. In addition, the second delayedfluorescent dopant has relatively narrow FWHM as compared to the firstdelayed fluorescent dopant. As a result, the OLED 400 can enhance itsluminous efficiency and color purity. As the exciton energy generated atthe first delayed fluorescent dopant in the EML1 462 is efficientlytransferred to the second delayed fluorescent dopant in the EML2 464,the OLED 400 can implement hyper-fluorescence.

The first delayed fluorescent dopant only transfers exciton energy tothe second delayed fluorescent dopant. Accordingly, the EML1 462including the first delayed fluorescent dopant is not involved in theultimate light emission process, but the ultimate light emission occursin the EML2 464 including the second delayed fluorescent dopant.

Each of the EML1 462 and the EML2 464 includes a first host and a secondhost, respectively. For example, each of the first host and the secondhost may respectively include, but is not limited to, mCP-CN, CBP, mCBP,mCP, DPEPO, PPT, TmPyPB, PYD-2CZ, DCzDBT, DCzTPA, pCzB-2CN, mCzB-2CN,TPSO1, CCP, 4-(3-(triphenylen-2-yl)phenyl)dibenzo[b,d]thiophene,9-(4-(9H-carbazol-9-yl)phenyl)-9H-3,9′-bicarbazole,9-(3-(9H-carbazol-9-yl)phenyl)-9H-3,9′-bicarbazole and/or9-(6-(9H-carbazol-9-yl)pyridin-3-yl)-9H-3,9′-bicarbazole.

Each of the first and second delayed fluorescent dopants that may beincluded in the EML1 462 or EML2 464 is not particularly limited as longas they satisfy the above-mentioned relationships in Equations (1) to(8). As an example, the first delayed fluorescent dopant may include anycompound having the structure of Chemical Formulae 1 to 3 and the seconddelayed fluorescent dopant may include any compound having the structureof Chemical Formulae 4 to 6.

In one exemplary embodiment, each of the first and second hosts may havea higher weight ratio than the first and second delayed fluorescentdopants in the EML1 462 and the EML2 464, respectively. In addition, theweight ratio of the first delayed fluorescent dopant in the EML1 462 maybe higher than the weight ratio of the second delayed fluorescent dopantin the EML2 464. In this case, it is possible to transfer enough energyfrom the first delayed fluorescent dopant in the EML1 462 to the seconddelayed fluorescent dopant in the EML2 464 by the FRET transfermechanism.

As an example, each of the EML1 462 and the EML2 464 may include each ofthe first host and the second host of about 50 to about 80% by weight,preferably about 60 to about 90% by weight. Further, each of the EML1462 and the EML2 464 may include each of the first delayed fluorescentdopant and the second delayed fluorescent dopant of about 10 to about50% by weight, preferably about 20 to about 40% by weight.

Energy level relationships among the luminous materials in thedouble-layered EML 460 will be explained. FIG. 8 is a schematic diagramillustrating luminous mechanism by energy level bandgap among luminousmaterials in a double-layered EML in accordance with another exemplaryembodiment of the present disclosure. As illustrated in FIG. 8, each ofan excited state singlet energy level S₁ ^(H1) and an excited statetriplet energy level T₁ ^(H1) of the first host is higher than anexcited state singlet energy level S₁ ^(TD1) and an excited statetriplet energy level T₁ ^(TD1) of the first delayed fluorescent dopantin the EML1 462, respectively. In addition, each of an excited statesinglet energy level S₁ ^(H2) and an excited state triplet energy levelT₁ ^(HD) of the second host is higher than an excited state singletenergy level S₁ ^(TD2) and an excited state triplet energy level T₁^(TD2) of the second delayed fluorescent dopant in the EML4 464,respectively. Alternatively, each of the excited state singlet energylevel S₁ ^(H2) and the excited state triplet energy level T₁ ^(2H) ofthe second host in the EML2 464 may be higher than the excited statesinglet energy level S₁ ^(TD1) and the excited state triplet energylevels T₁ ^(TD1) of the first delayed fluorescent dopant in the EML1462, respectively.

In addition, each of the excited state singlet energy level S₁ ^(TD1)and the excited state triplet energy levels T₁ ^(TD1) of the firstdelayed fluorescent dopant in the EML1 462 is higher than each of theexcited state singlet energy level S₁ ^(TD2) and the excited statetriplet energy level T₁ ^(TD2) of the second delayed fluorescent dopantin the EML2 464, respectively.

When the luminous materials do not satisfy the above-described energylevel relationships, exciton quenching as non-emission excitonannihilation occurs at the first and/or second delayed fluorescentdopants, or exciton energy cannot be efficiently transferred from thehost to the dopants so that the luminous efficiency of the OLED 400 maybe deteriorated.

In an alternatively exemplary embodiment, the second host, which isincluded in the EML2 464 together with the second delayed fluorescentdopant, may be the same material as the HBL 475. In this case, the EML2464 may have a hole blocking function as well as an emission function.In other words, the EML2 464 can act as a buffer layer for blockingholes. In one embodiment, the HBL 475 may also be omitted, in particularwhen the EML2 464 is a hole blocking layer as well as an emittingmaterial layer.

In another exemplary embodiment, the EML1 462 may include the secondhost and the second delayed fluorescent dopant and the EML2 464 mayinclude the first host and the first delayed fluorescent dopant. In thisembodiment, the second host in the EML1 462 may be the same material asthe EBL 455. In this case, the EML1 462 may have an electron blockingfunction as well as an emission function. In other words, the EML1 462can act as a buffer layer for blocking electrons. In one embodiment, theEBL 455 may be omitted where the EML1 462 may be an electron blockinglayer as well as an emitting material layer.

An OLED having a triple-layered EML will be explained. FIG. 9 is across-sectional view illustrating an organic light emitting diode havinga triple-layered EML in accordance with another exemplary embodiment ofthe present disclosure. As illustrated in FIG. 10, an OLED 500 inaccordance with a fourth embodiment of the present disclosure includesfirst and second electrodes 510 and 520 facing each other and anemitting unit 530 as an emissive unit disposed between the first andsecond electrodes 510 and 520.

In one exemplary embodiment, the emitting unit 530 includes an HIL 540,an HTL 550, an EML 560, an ETL 570 and an EIL 580 each of which islaminated sequentially over the first electrode 510. Besides, theemitting unit 530 may further include an EBL 555 as a first excitonblocking layer disposed between the HTL 550 and the EML 560, and/or anHBL 575 as a second exciton blocking layer disposed between the EML 560and the ETL 570.

The OLED 500 in accordance with the third embodiment may have the samefirst and second electrodes 510 and 520 as the OLEDs 300 and 400 inaccordance with the first to third embodiments. The emitting unit 530may also be the same except for the EML 560.

The first electrode 510 may be an anode and may include, but is notlimited to, a conductive material having a relatively large workfunction values such as ITO, IZO, SnO, ZnO, ICO, AZO, and the likes. Thesecond electrode 520 may be a cathode and may include, but is notlimited to, a conductive material having a relatively small workfunction values such as Al, Mg, Ca, Ag, alloys thereof or combinationsthereof.

The HIL 540 is disposed between the first electrode 510 and the HTL 550.The HIL 540 may include, but is not limited to, MTDATA, NATA, 1T-NATA,2T-NATA, CuPc, TCTA, NPB(NPD), HAT-CN, TDAPB, PEDOT/PSS and/orN-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine.The HIL 540 may be omitted in accordance with the structure of the OLED500.

The HTL 550 is disposed adjacently to the EML 560 between the firstelectrode 510 and the EML 560. The HTL 550 may include, but is notlimited to, aromatic amine compounds such as TPD, NPD(NPB), CBP,poly-TPD, TFB, TAPC,N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amineand/orN-(biphenyl-4-yl)-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)biphenyl-4-amine.

The EBL 555 may include, but is not limited to, TCTA,Tris[4-(diethylamino)phenyl]amine,N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluorene-2-amine,TAPC, MTDATA, mCP, mCBP, CuPc,N,N′-bis[4-(bis(3-methylphenyl)amino)phenyl]-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(DNTPD), TDAPB and/or 3,6-bis(N-carbazolyl)-N-phenyl-carbazole.

The EML 560 includes a first EML (EML1) 562, a second EML (EML2) 564 anda third EML (EML3) 566. The configuration and energy levels among theluminous materials in the EML 560 will be explained in more detailbelow.

The HBL 575 may include, but is not limited to, oxadiazole-basedcompounds, triazole-based compounds, phenanthroline-based compounds,benzoxazole-based compounds, benzothiazole-based compounds,benzimidazole-based compounds, and triazine-based compounds. As anexample, the HBL 575 may include a compound having a relatively low HOMOenergy level compared to the emitting material in EML 560. The HBL 575may include, but is not limited to, BCP, BAlq, Alq₃, PBD, spiro-PBD,Liq, B3PYMPM, DPEPO,9-(6-(9H-carbazol-9-yl)pyridine-3-yl)-9H-3,9′-bicarbazole andcombinations thereof.

The ETL 570 is disposed between the EML 560 and the EIL 580. In oneexemplary embodiment, the ETL 570 may include, but is not limited to,oxadiazole-based compounds, triazole-based compounds,phenanthroline-based compounds, benzoxazole-based compounds,benzothiazole-based compounds, benzimidazole-based compounds,triazine-based compounds, and the likes. As an example, the ETL 570 mayinclude, but is not limited to, Alq₃, PBD, spiro-PBD, Liq, TPBi, BAlq,Bphen, NBphen, BCP, TAZ, NTAZ, TpPyPB, TmPPPyTz, PFNBr and/or TPQ.

The EIL 580 is disposed between the second electrode 520 and the ETL570. In one exemplary embodiment, the EIL 580 may include, but is notlimited to, an alkali halide such as LiF, CsF, NaF, BaF₂ and the likes,and/or an organic metal compound such as lithium benzoate, sodiumstearate, and the likes.

As described above, the EML 560 includes the EML1 562 disposed betweenthe EBL 555 and the HBL 575, the EML2 564 disposed between the EML1 562and the HBL 575 and the EML3 566 disposed between the EML2 564 and theHBL 575. In one exemplary embodiment, each of the EML1 562 and the EML3566 may include the delayed fluorescent material of any compound havingthe structure in Chemical Formulae 1 to 3, and the EML2 564 may includethe delayed fluorescent material of any compound having the structure inChemical Formulae 4 to 6. In another exemplary embodiment, each of theEML1 562 and the EMl3 566 may include the delayed fluorescent materialof any compound having the structure in Chemical Formulae 4 to 6, andthe EML2 564 may include the delayed fluorescent material of anycompound having the structure in Chemical Formulae 1 to 3. Hereinafter,the EML 560, where each of the EML1 562 and the EML3 566 includes thedelayed fluorescent material of any compound having the structure inChemical Formulae 1 to 3 and the EML2 564 include the delayedfluorescent material of any compound having the structure in ChemicalFormulae 4 to 6, will be explained. For example, each of the EML1 toEML3 562, 564 and 566 may include first to third delayed fluorescentdopant, respectively. In this case, each of the first and third delayedfluorescent dopant may be an organic compound having an electron donormoiety and an electron acceptor moiety. In addition, each of the EML1 toEML3 562, 564 and 566 may further include first to third hosts,respectively.

In accordance with this embodiment, the singlet and triplet excitonenergies of the first and third delayed fluorescent dopants, each ofwhich is included in the EML1 562 and the EML3 566, is transferred tothe second delayed fluorescent dopant, which is included in the EML2 564disposed adjacently to the EML1 562 and the EML3 566, by the FRET energytransfer mechanism. Accordingly, the ultimate emission occurs in thesecond delayed fluorescent dopant in the EML2 564.

In other words, the triplet exciton energy of the first and thirddelayed fluorescent dopants is converted to the singlet exciton energyof their own in the EML1 562 and the EML3 566 by the RISC mechanism,then the singlet exciton energy of the first and third delayedfluorescent dopants is transferred to the singlet exciton energy of thesecond delayed fluorescent dopant in the EML2 564 because the excitedstate singlet energy levels S₁ ^(TD1) and S₁ ^(TD3) of the first andthird delayed fluorescent dopants in the EML1 562 and the EML3 566 arehigher than the excited state singlet energy levels S₁ ^(TD2) of thesecond delayed fluorescent dopant in the EML2 564 (See, FIG. 10).

The second delayed fluorescent dopant in the EML2 564 can emit lightusing the singlet exciton energy and the triplet exciton energy derivedfrom the first and third delayed fluorescent dopants in the EML1 562 andthe EMl3 566. Therefore, the OLED 500 has an enhanced luminousefficiency and color purity which is also due to the narrow FWHM of thesecond delayed fluorescent dopant.

In this case, the first and third delayed fluorescent dopants onlytransfer energy to the second delayed fluorescent dopant. The EML1 562and the EML3 566 including the first and third delayed fluorescentdopants is not involved in the ultimate emission process, while EML2 564including the second delayed fluorescent dopant emits light. Since thesecond delayed fluorescent dopant have relatively narrow FWHM ascompared to the first and third delayed fluorescent dopant, the OLED 500has an enhanced luminous efficiency and color purity.

In addition, each of the EML1 562, the EML2 564 and the EML3 566 includethe first host, the second host and the third host, respectively. Thefirst to third hosts are the same as or different from one another. Asan example, each of the first to third host may independently include,but is not limited to, mCP-CN, CBP, mCBP, mCP, DPEPO, PPT, TmPyPB,PYD-2CZ, DCzDBT, DCzTPA, pCzB-2CN, mCzB-2CN, TPSO1, CCP,4-(3-(triphenylen-2-yl)phenyl)dibenzo[b,d]thiophene,9-(4-(9H-carbazol-9-yl)phenyl)-9H-3,9′-bicarbazole,9-(3-(9H-carbazol-9-yl)phenyl)-9H-3,9′-bicarbazole and/or9-(6-(9H-carbazol-9-yl)pyridin-3-yl)-9H-3,9′-bicarbazole.

Each of the first and third delayed fluorescent dopants that may beincluded in the EML1 562 and the EML3 566 is not particularly limited aslong as they satisfy the above-mentioned relationships in Equations (1)to (8). As an example, each of the first and third delayed fluorescentdopant may include any compound having the structure in Chemical Formula1 to 3 and the second delayed fluorescent dopant may include anycompound having the structure in Chemical Formulae 4 to 6.

In one exemplary embodiment, each of the first to third hosts may have ahigher weight ratio than the first to third delayed fluorescent dopantsin the EML1 562, the EML2 564 and the EML3 566, respectively. Inaddition, the weight ratio of each of the first and third delayedfluorescent dopants in the EML1 562 and the EML3 566 may be higher thanthe weight ratio of the second delayed fluorescent dopant in the EML2564, respectively. In this case, it is possible to transfer enoughenergy from the first and third delayed fluorescent dopants in the EML1562 and the EML 566 to the second delayed fluorescent dopants in theEML2 564.

As an example, each of the EML1 562 to the EML3 566 may include each ofthe first to third hosts of about 50 to about 90% by weight, preferablyabout 60 to about 80% by weight, respectively. Further, each of the EML562 to the EML3 666 may include each of the first to third delayedfluorescent dopants of about 10 to about 50% by weight, preferably about20 to about 40% by weight, respectively.

Energy level relationships among the luminous materials in the EML 560will be explained in more detail. FIG. 10 is a schematic diagramillustrating luminous mechanism by energy level bandgap among theluminous material in a triple-layered EML in accordance with anotherexemplary embodiment of the present disclosure. As illustrated in FIG.10, each of excited state singlet energy levels S₁ ^(H1), S₁ ^(H1) andS₁ ^(H3) and excited state triplet energy level T₁ ^(H1), T₁ ^(H2) andT₁ ^(H3) of the first to third hosts is higher than excited statesinglet energy levels S₁ ^(TD1), S₁ ^(TD2) and S₁ ^(TD3) and excitedstate triplet energy levels T₁ ^(TD1), T₁ ^(TD2) and T₁ ^(TD3) of thefirst to third delayed fluorescent dopants in the EML1 562, EML2 564,EML3 566, respectively. In addition each of the excited state singletenergy levels S₁ ^(TD1) and S₁ ^(TD3) and the excited state tripletenergy levels T₁ ^(TD1) and T₁ ^(TD3) of the first and third delayedfluorescent dopants in the EML1 562 and the EML3 566 is higher than eachof the excited state singlet energy levels S₁ ^(TD2) and excited statetriplet energy levels T₁ ^(TD2) of the second delayed fluorescent dopantin the EML2 564, respectively.

When the luminous materials do not satisfy the above-described energylevel relationships, exciton quenching as non-emission excitonannihilation occurs at the first and/or second delayed fluorescentdopants, or exciton energy cannot be efficiently transferred from thehost to the dopants so that luminous efficiency of the OLED 500 may bedeteriorated.

In an alternatively exemplary embodiment, the first host, which isincluded in the EML1 562 together with the first delayed fluorescentdopant, may be the same material as the EBL 555. In this case, the EML1562 may have an electron blocking function as well as an emissionfunction. In other words, the EML2 562 can act as a buffer layer forblocking electrons. In one embodiment, the EBL 555 may also be omitted,in particular when the EML1 562 is an electron blocking layer as well asan emitting material layer.

In another exemplary embodiment, the third host, which is included inthe EML3 566 together with the third delayed fluorescent dopant, may bethe same material as the HBL 575. In this case, the EML3 566 may have ahole blocking function as well as an emission function. In other words,the EML3 566 can act as a buffer layer for blocking holes. In oneembodiment, the HBL 575 may also be omitted, in particular when the EML3566 is a hole blocking layer as well as an emitting material layer.

In still another exemplary embodiment, the first host in the EML1 562may be the same material as the EBL 555 and the third host in the EML3566 may be the same material as the HBL 575. In this embodiment, theEML1 562 may have an electron blocking function as well as an emissionfunction, and the EML3 566 may have a hole blocking function as well asan emission function. In other words, each of the EML1 562 and the EML3566 can act as a buffer layer for blocking electrons or holes,respectively. In one embodiment, the EBL 555 and the HBL 575 may beomitted, in particular when the EML1 562 is an electron blocking layeras well as an emitting material layer and the EML3 566 is a holeblocking layer as well as an emitting material layer.

In the above embodiments, the OLED having only one emitting unit isdescribed. Unlike the above embodiment, the OLED may have multipleemitting units so as to form a tandem structure. FIG. 11 is across-sectional view illustrating an organic light emitting diode inaccordance with still another embodiment of the present disclosure.

As illustrated in FIG. 11, the OLED 600 in accordance with the fourthembodiment of the present disclosure includes first and secondelectrodes 610 and 620 facing each other, a first emitting unit 630 as afirst emission layer disposed between the first and second electrodes610 and 620, a second emitting unit 730 as a second emission layerdisposed between the first emitting unit 630 and the second electrode620, and a charge generation layer 800 disposed between the first andsecond emitting units 630 and 730.

As mentioned above, the first electrode 610 may be an anode and mayinclude, but is not limited to, a conductive material, for example, atransparent conductive material (TCO), having a relatively large workfunction value. As an example, the first electrode 610 may include, butis not limited to, ITO, IZO, SnO, ZnO, ICO, AZO, and the likes. Thesecond electrode 620 may be a cathode and may include, but is notlimited to, a conductive material having a relatively small workfunction values such as Al, Mg, Ca, Ag, alloys thereof or combinationsthereof.

The first emitting unit 630 includes a HIL 640, a first HTL (a lowerHTL) 650, a lower EML 660 and a first ETL (a lower ETL) 670. The firstemitting unit 630 may further include a first EBL (a lower EBL) 655disposed between the first HTL 650 and the lower EML 660 and/or a firstHBL (a lower HBL) 675 disposed between the lower EML 660 and the firstETL 670.

The second emitting unit 730 includes a second HTL (an upper HTL) 750,an upper EML 760, a second ETL (an upper ETL) 770 and an EIL 780. Thesecond emitting unit 730 may further include a second EBL (an upper EBL)755 disposed between the second HTL 750 and the upper EML 760 and/or asecond HBL (an upper HBL) 775 disposed between the upper EML 760 and thesecond ETL 770.

At least one of the lower EML 660 and the upper EML 760 may emit blue(B) light. As an example, both the lower and upper EMLs 660 and 760 mayemit blue light. Alternatively, one of the lower and upper EMLs 660 and760 may emit blue light and the other of the lower and upper EMLs 660and 760 may emit any other light having emission wavelength rangeslonger than the blue light, for example, green (G), yellow-green (YG),yellow (Y) and/or Orange. Hereinafter, the OLED 600, where the lower EML660 emits blue light and the upper EML 760 emits green, yellow-green,yellow and/or orange light, will be explained.

The HIL 640 is disposed between the first electrode 610 and the firstHTL 650 and improves an interface property between the inorganic firstelectrode 610 and the organic first HTL 650. In one exemplaryembodiment, the HIL 640 may include, but is not limited to, MTDATA,NATA, 1T-NATA, 2T-NATA, CuPc, TCTA, NPB(NPD), HAT-CN, TDAPB, PEDOT/PSSand/orN-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine.The HIL 640 may also be omitted in accordance with an inventivestructure of the OLED 600.

Each of the first and second HTLs 650 and 750 may independently include,but is not limited to, TPD, NPD(NPB), CBP, poly-TPD, TFB, TAPC,N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amineand/orN-(biphenyl-4-yl)-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)biphenyl-4-amine.

Each of the first and second ETLs 670 and 770 facilitates electrontransportations in the first emitting unit 630 and the second emittingunit 730, respectively. Each of the first and second ETLs 670 and 770may independently include, but is not limited to, oxadiazole-basedcompounds, triazole-based compounds, phenanthroline-based compounds,benzoxazole-based compounds, benzothiazole-based compounds,benzimidazole-based compounds, triazine-based compounds, and the likes,respectively. As an example, each of the first and second ETLs 670 and770 may independently include, but is not limited to, Alq₃, PBD,spiro-PBD, Liq, TPBi, BAlq, Bphen, NBphen, BCP, TAZ, NTAZ, TpPyPB,TmPPPyTz, PFNBr and/or TPQ, respectively.

The EIL 780 is disposed between the second electrode 620 and the secondETL 770, and can improve physical properties of the second electrode 620and therefore, can enhance the life span of the OLED 600. In oneexemplary embodiment, the EIL 680 may include, but is not limited to, analkali halide such as LiF, CsF, NaF, BaF₂ and the likes, and/or anorganic metal compound such as lithium benzoate, sodium stearate, andthe likes.

Each of the first and second EBLs 655 and 755 may independently include,but is not limited to, TCTA, Tris[4-(diethylamino)phenyl]amine,N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluorene-2-amine,TAPC, MTDATA, mCP, mCBP, CuPc,N,N′-bis[4-(bis(3-methylphenyl)amino)phenyl]-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(DNTPD), TDAPB and/or 3,6-bis(N-carbazolyl)-N-phenyl-carbazole,respectively.

Each of the first and second HBLs 675 and 775 may independently include,but is not limited to, oxadiazole-based compounds, triazole-basedcompounds, phenanthroline-based compounds, benzoxazole-based compounds,benzothiazole-based compounds, benzimidazole-based compounds, andtriazine-based compounds. As an example, each of the first and secondHBLs 675 and 775 may independently include, but is not limited to, BCP,BAlq, Alq₃, PBD, spiro-PBD, Liq, B3PYMPM, DPEPO,9-(6-(9H-carbazol-9-yl)pyridine-3-yl)-9H-3,9′-bicarbazole andcombinations thereof, respectively.

In one exemplary embodiment, when the upper EML 760 emits green light,the upper EML 760 may be, but is not limited to, a phosphorescentemitting material layer that includes a host (e.g. CBP and the likes)and an iridium-based dopant (e.g. Iridium (III)bis(2,4-diphenyloxazolato-1,3-N,C2′)(acetyl acetonate) (dpo₂Ir(acac)),Iridium (III) bis(2-phenyl-oxazolinato-N,C2′)(acetyl acetonate)(op₂Ir(acac)) and the likes). Alternatively, the upper EML 760 may be afluorescent material including Alq as a dopant. In this case, the upperEML 760 may emit green light having, but is not limited to, emissionwavelength ranges of about 510 nm to about 570 nm.

In another exemplary embodiment, when the upper EML 760 emits yellowlight, the upper EML 760 may have a single-layered structure ofyellow-green EML or a double-layered structure of a yellow-green EML andgreen EML. As an example, when the upper EML 760 is a yellow-green EML,the upper EML 760 may include, but is not limited to, a host selectedfrom at least one of CBP and BAlq and a phosphorescent dopant emittingyellow-green light. In this case, the upper EML 760 may emityellow-green light having, but is not limited to, emission wavelengthranges of about 510 nm to about 590 nm.

In still another exemplary embodiment, the upper EML 760 may have twoEMLs, for example, a yellow-green EML and a red EML. As an example, whenthe upper EML 760 is a yellow-green EML, the upper EML 760 may have asingle-layered structure of yellow-green EML or a double-layeredstructure of a yellow-green EML and a green EML. When the upper EML 760has a single-layered structure of the yellow-green EML, the upper EML760 may include, but is not limited to, a host selected from at leastone of CBP and BAlq and a phosphorescent dopant emitting yellow-greenlight.

The charge generation layer (CGL) 800 is disposed between the firstemitting unit 630 and the second emitting unit 730. The CGL 800 includesan N-type CGL 810 disposed adjacently to the first emitting unit 630 anda P-type CGL 820 disposed adjacently to the second emitting unit 730.The N-type CGL 810 injects electrons into the first emitting unit 630and the P-type CGL 820 injects holes into the second emitting unit 730.

As an example, the N-type CGL 810 may be a layer doped with an alkalimetal such as Li, Na, K and/or Cs and/or an alkaline earth metal such asMg, Sr, Ba and/or Ra. For example, a host used in the N-type CGL 810 mayinclude, but is not limited to, an organic compound such as Bphen orMTDATA. The alkali metal or the alkaline earth metal may be doped byabout 0.01 wt % to about 30 wt %.

The P-type CGL 820 may include, but is not limited to, an inorganicmaterial selected from the group consisting of tungsten oxide (WO_(x)),molybdenum oxide (MoO_(x)), beryllium oxide (Be₂O₃), vanadium oxide(V₂O₅) and combinations thereof, and/or an organic material selectedfrom the group consisting of NPD, HAT-CN,2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), TPD,N,N,N′,N′-Tetranaphthalenyl-benzidine (TNB), TCTA,N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) and combinationsthereof.

The lower EML 660 includes a first EML (EML1) 662, a second EML (EML2)664 and a third EML3 (EML3) 666. The EML1 662 is disposed between thefirst EBL 655 and the first HBL 675, the EML2 664 is disposed betweenthe first EML 662 and the first HBL 675 and the EML3 666 disposedbetween the EML2 664 and the first HBL 675. Each of the EML1 662 to EML3666 includes the first to third delayed fluorescent dopants,respectively. Each of the EML1 662, EML2 664 and EML3 666 furtherincludes a first host, a second host and a third host, respectively.

In one exemplary embodiment, each of the EML1 662 and the EML3 666 mayinclude the delayed fluorescent material of any compound having thestructure in Chemical Formulae 1 to 3, and the EML2 664 may include thedelayed fluorescent material of any compound having the structure inChemical Formulae 4 to 6. In another exemplary embodiment, each of theEML1 662 and the EMl3 666 may include the delayed fluorescent materialof any compound having the structure in Chemical Formulae 4 to 6, andthe EML2 664 may include the delayed fluorescent material of anycompound having the structure in Chemical Formulae 1 to 3. Hereinafter,the lower EML 660, where each of the EML1 662 and the EML3 666 includesthe delayed fluorescent material of any compound having the structure inChemical Formulae 1 to 3 and the EML2 664 include the delayedfluorescent material of any compound having the structure in ChemicalFormulae 4 to 6, will be explained. For example, each of the EML1 toEML3 662, 664 and 666 may include first to third delayed fluorescentdopant, respectively. In this case, each of the first and third delayedfluorescent dopant may be an organic compound having an electron donormoiety and an electron acceptor moiety. In addition, each of the EML1 toEML3 662, 664 and 666 may further include first to third hosts,respectively.

The singlet and triplet exciton energies of the first and third delayedfluorescent dopant, which is included in the EML1 662 and the EML3 666,is transferred to the second delayed fluorescent dopant, which isincluded in the EML2 664 disposed adjacently to the EML1 662 by the FRETenergy transfer mechanism. Accordingly, the ultimate emission occurs inthe second delayed fluorescent dopant in the EML2 664.

In other words, the triplet exciton energy of the first and thirddelayed fluorescent dopants is converted to the singlet exciton energyof their own in the EML1 662 and the EML3 666 by the RISC mechanism,then the singlet exciton energy of the first and third delayedfluorescent dopants is transferred to the singlet exciton energy of thesecond delayed fluorescent dopant because the excited state singletenergy levels S₁ ^(TD1) and S₁ ^(TD3) of the first and third delayedfluorescent dopants in the EML1 662 and the EML3 666 are higher than theexcited state singlet energy levels S₁ ^(TD1) of the second delayedfluorescent dopant in the EML2 664 (See, FIG. 10).

The second delayed fluorescent dopant in the EML2 664 can emit lightusing the singlet exciton energy and the triplet exciton energy derivedfrom the first and third delayed fluorescent dopants in the EML1 662 andthe EML3 666. Therefore, the OLED 600 has an enhanced luminousefficiency and color purity also due to the narrow FWHM of the seconddelayed fluorescent dopant.

In addition, each of the EML1 662, the EML2 664 and the EML3 666 includethe first host, the second host and the third host, respectively. Thefirst to third hosts are the same as or different from one another. Asan example, each of the first to third host may independently include,but is not limited to, mCP-CN, CBP, mCBP, mCP, DPEPO, PPT, TmPyPB,PYD-2CZ, DCzDBT, DCzTPA, pCzB-2CN, mCzB-2CN, TPSO1, CCP,4-(3-(triphenylen-2-yl)phenyl)dibenzo[b,d]thiophene,9-(4-(9H-carbazol-9-yl)phenyl)-9H-3,9′-bicarbazole,9-(3-(9H-carbazol-9-yl)phenyl)-9H-3,9′-bicarbazole and/or9-(6-(9H-carbazol-9-yl)pyridin-3-yl)-9H-3,9′-bicabazole.

Each of the first and third delayed fluorescent dopants that may beincluded in the EML1 562 and the EML3 566 is not particularly limited aslong as they satisfy the above-mentioned relationships in Equations (1)to (8). As an example, each of the first and third delayed fluorescentdopant may include any compound having the structure in ChemicalFormulae 1 to 3 and the second delayed fluorescent dopant may includeany compound having the structure in Chemical Formulae 4 to 6.

In this case, the energy level relationships among the luminousmaterials, i.e. the first to third hosts, and the first to third delayedfluorescent dopants in the EML 660 may be in the same way as illustratedin FIG. 10.

In one exemplary embodiment, each of the first to third hosts isincluded in a higher weight ratio than the first to third delayedfluorescent dopants in the EML1 662, the EML2 664 and the EML3 666,respectively. In addition, the weight ratio of each of the first andthird delayed fluorescent dopants in the EML1 662 and the EML3 666 maybe higher than the weight ratio of the second delayed fluorescent dopantin the EML2 664, respectively. In this case, it is possible to transferenough energy from the first and third delayed fluorescent dopants inthe EML1 662 and the EML 666 to the second delayed fluorescent dopantsin the EML2 664.

In an alternatively exemplary embodiment, the first host, which isincluded in the EML1 662 together with the first delayed fluorescentdopant, may be the same material as the first EBL 655. In this case, theEML1 662 may have an electron blocking function as well as an emissionfunction. In other words, the EML1 664 can act as a buffer layer forblocking electrons. In one embodiment, the first EBL 655 may also beomitted, in particular when the EML1 662 is an electron blocking layeras well as an emitting material layer.

In another exemplary embodiment, the third host, which is included inthe EML3 666 together with the third delayed fluorescent dopant, may bethe same material as the first HBL 675. In this case, the EML3 666 mayhave a hole blocking function as well as an emission function. In otherwords, the EML3 666 can act as a buffer layer for blocking holes. In oneembodiment, the first HBL 675 may also be omitted, in particular whenthe EML3 666 is a hole blocking layer as well as an emitting materiallayer.

In still another exemplary embodiment, the first host in the EML1 662may be the same material as the first EBL 655 and the third host in theEML3 666 may be the same material as the first HBL 675. In thisembodiment, the EML1 662 may have an electron blocking function as wellas an emission function, and the EML3 666 may have a hole blockingfunction as well as an emission function. In other words, each of theEML1 662 and the EML3 666 can act as a buffer layer for blockingelectrons or hole, respectively. In one embodiment, the first EBL 655and the first HBL 675 may also be omitted, in particular when the EML1662 is an electron blocking layer as well as an emitting material layerand the EML3 666 is a hole blocking layer as well as an emittingmaterial layer.

In an alternative embodiment, the lower EML 660 may have asingle-layered structure as illustrated in FIG. 2. In this case, thelower EML 660 may include a host and first and second delayedfluorescent dopants. In another alternative embodiment, the lower EML660 may have a double-layered structure as illustrated in FIG. 7. Inthis case, the lower EML 660 may include a first EML and a second EML.The first EML may include a first host and a first delayed fluorescentdopant, and the second EML may include a second host and a seconddelayed fluorescent dopant.

In still another exemplary embodiment, an OLED of the present disclosuremay further include a third emitting unit (not shown) disposed betweenthe second emitting unit 730 and the second electrode 620 and a secondCGL (not shown) disposed between the second emitting unit 730 and thethird emitting unit (not shown). In this case, at least one of the firstemitting unit 630, the second emitting unit 730 and the third emittingunit (not shown) may include an emitting material layer which includesat least one host and first and second fluorescent dopants, as describedabove.

Synthesis Example 1: Synthesis of Compound A-1

(1) Synthesis of Intermediate 1A

20 g (119.6 mmol) of carbazole, 67.4 g (239.2 mmol) of 2-bromoiodobenzene, 11.4 g (59.8 mmol) of copper iodide and 33.1 g (239.2 mmol) ofpotassium carbonate were suspended in toluene, and then solution wasrefluxed with stirring for 12 hours. The solution was extracted withdichloromethane and water, the organic layer was dried with magnesiumsulfate and then was filtered with silica gel. The extracted liquid wasdistilled under reduced pressure and purified by column chromatographyto give 32.6 g (yield: 85%) of intermediate 1A.

(2) Synthesis of Intermediate 1B

After 6.4 g (20.0 mmol) of intermediate 1A was dissolved in 70 mL ofTHF, the solution was cooled down −78° C. 8.8 mL (22 mmol) of n-BuLi(2.5 M in hexane) was injected slowly into the solution. The mixedsolution was stirred for 2 hours, was cooled down −78° C. again, andthen 5.6 g (30 mmol) of tri-isopropyl borate was injected into the mixedsolution. After stirring for 5 hours at room temperature, the solutionwas quenched with 1N HCl. The solution was extracted with ethyl acetateand water, the organic layer was dried with magnesium sulfate and thenwas filtered with silica gel. The extracted liquid was distilled underreduced pressure and purified by column chromatography to give 3.8 g(yield: 68%) of intermediate 1B.

-   -   (3) Synthesis of Compound A-1

5.7 g (20 mmol) of intermediate 1B, 5.3 g (20 mmol) of2-chloro-4,6-diphenyl-1,3,6-triazine, 0.7 g (0.6 mmol) oftetrakis(triphenylphosphine) palladium (0) (Pd(PPh₃)₄) and 8.3 g (60mmol) of potassium carbonate was suspended of a mixed solvent of 75 mLof THF and 15 mL of water, and then the solution was refluxed undernitrogen atmosphere. The solution was extracted with dichloromethane andwater, the organic layer was dried with magnesium sulfate and then wasfiltered with

silica gel. The extracted liquid was distilled under reduced pressureand purified by column chromatography to give 5.6 g (yield: 60%) ofCompound A-1.

Synthesis Example 2: Synthesis of Compound A-2

(1) Synthesis of Intermediate 2A

10 g (41 mmol) of 3-bromo carbazole and 1.8 g (45 mmol) of sodiumhydroxide was added into 100 mL of dimethyl sulfoxide (DMF), and then7.4 g (43 mmol) of benzyl bromide was injected with drop-wise into thesolution with stirring under nitrogen atmosphere. After stirring for 20hours at room temperature, the solution was extracted withdichloromethane and water, the organic layer was dried with magnesiumsulfate and then was filtered with silica gel. The extracted liquid wasdistilled under reduced pressure and purified by column chromatographyto give 11 g (yield: 80%) of intermediate 2A.

(2) Synthesis of Intermediate 2B

4.47 g (13.3 mmol) of intermediate 2A, 0.69 g (0.67 mmol) oftris(dibenzylideneacetone) dipalladium (0) chloroform complex(Pd₂(dba)₃.CH₃Cl) 0.82 g (2.7 mmol) of tri-tert-butylphosphoniumtetrafluoroborate (P(t-Bu)₃.HFB₄), 1.9 g (20 mmol) of sodium t-butoxide(tert-BuONa) and 2.5 g (14.6 mmol) of diphenyl amine were dissolved indry toluene, and then the solution was refluxed with stirring for 18hours at 100° C. under nitrogen atmosphere. The solution was extractedwith dichloromethane and water, the organic layer was dried withmagnesium sulfate and then was filtered with silica gel. The extractedliquid was distilled under reduced pressure and purified by columnchromatography to give 4.3 g (yield: 76%) of intermediate 2B.

(3) Synthesis of Intermediate 2C

After 6.3 g (15.0 mmol) of intermediate 2B was dispersed in 45 mLanisole, and 12.0 g (90.0 mmol) of AlCl₃ was injected into the anisolesuspension slowly. After stirring for 24 hours at 65° C., the solutionwas extracted with dichloromethane and water, the organic layer wasdried with magnesium sulfate and then was filtered. The extracted liquidwas distilled under reduced pressure and purified by columnchromatography to give 2.3 g (yield: 46%) of intermediate 2C.

(4) Synthesis of Intermediate 2D

5.3 g (20 mmol) of 2-chloro-4,6-diphenyl-1.3,5-triazine, 4.4 g (22 mmol)of 2-bromophenyl boronic acid, 8.3 g (60 mmol) of potassium carbonateand 0.7 g (0.6 mmol) of Pd(PPh₃)₄ were suspended into a mixed solvent of75 mL of THF and 15 mL of water, and then the suspension was refluxedwith stirring for 12 hours under nitrogen atmosphere. The solution wasextracted with dichloromethane and water, the organic layer was driedwith magnesium sulfate and then filtered with silica gel. The extractedliquid was distilled under reduced pressure and purified by columnchromatography to give 5.0 g (yield: 65%) of intermediate 2D.

(5) Synthesis of Compound A-2

5.0 g (15.0 mmol) of intermediate 2C, 6.4 g (16.5 mmol) of intermediate2D, 0.78 g (0.75 mmol) of Pd₂(dba)₃.CHCl₃, 0.91 g (3.0 mmol) ofP(t-Bu)₃.HBF₄, 2.2 g (22.5 mmol) of tert-BuONa were dissolved in 100 mLof dry toluene, and then the solution was refluxed with stirring for 18hours at 100° C. under nitrogen atmosphere. The solution was extractedwith dichloromethane and water, the organic layer was dried withmagnesium sulfate and then was filtered with silica gel. The extractedliquid was distilled under reduced pressure and purified by columnchromatography to give 5.8 g (yield: 60%) of Compound A-2.

Synthesis Example 3: Synthesis of Compound B-1

(1) Synthesis of Intermediate 3A

50 g (0.29 mol) of diphenyl amine, 32.3 g (0.34 mol) of sodiumtert-butoxide (t-BuONa), 1.0 g (1.4 mmol) of dichlorobis[di-tert-butyl(p-dimethylaminophenyl) phosphine] palladium (II) (PdCl₂(Amphos)₂), 30 g(0.13 mol) of 1-bromo-2,3-dichlorobenzene were dissolved in 330 mL ofo-xylene under nitrogen atmosphere, and then the solution was stirredfor 2 hours at 80° C. and additionally stirred for 3 hours at 120° C.Then, the solution was treated with ethyl acetate and water to generatea precipitate. After the liquid was separated by filtering, the liquidwas dissolved in toluene, was passed through a silica gel column andthen distilled under reduced pressure to give 29 g (yield: 50%) ofintermediate 3A.

(2) Synthesis of Compound B-1

After 20 g (44.7 mmol) of intermediate 3A was dissolved in 150 mL oftert-butylbenzne, 31.6 mL (53.7 mmol) of 1.7 M tert-BuLi (in pentane)was injected with drop-wise at −30° C. After stirring for 2 hours at 60°C., pentane was evaporated, the solution was cooled down −30° C., 5.1 mL(53.9 mmol) of tri-bromide was injected into the solution, and then thesolution was stirred again for 30 minutes. 15.6 mL (90 mmol) ofN,N-diisopropyl amine was injected into the solution at 0° C., thetemperature was raised and the solution was stirred for 3 hours at 120°C. 100 mL of water (dissolving 13 g of sodium acetate) and 50 mL ofethyl acetate was added to the reaction vessel. The solution wasextracted with ethyl acetate, the organic layer was dried with magnesiumsulfate and then the solution was filtered. After the solution wasdistilled under reduced pressure, the solution was treated with tolueneand pentane to precipitate a solid 4 g (yield: 21%) of Compound B-1.

Experimental Example 1: Evaluation of Energy Level of Compound

Energy levels such as excited state singlet energy level (S₁), excitedstate triplet energy level (T₁), HOMO energy levels and LUMO energylevels were evaluated for compound A-1, A-2 and B-1 which have beensynthesized according to Synthesis Examples 1 to 3. In order to measurethe S₁ of the compounds, each of the compounds was deposited on a glasssubstrate with a thickness of 50 nm, and an absorption spectrum for thecompound was measured at 298K. A tangent line was drawn with respect tothe falling curve on the long wavelength sides of the measuredabsorption spectrum to obtain a wavelength value (λ_(edge); nm) at theintersection of the tangent line and the horizontal axis. Using thewavelength value, S₁ was calculated from the following ConversionEquation 1:S ₁ (eV)=1242/λ_(edge)  Conversion Equation 1

In order to measure the T1 of the compounds, a film of mCBP doped witheach of the compounds (doping concentration: 20%) was deposited on aglass substrate with a thickness of 50 nm and maximum photoluminescence(λ_(max)) of phosphorescent peak was measured using 355 nm beam at 77K.Using the λ_(max), T₁ was calculated from the following ConversionEquation 2:T ₁ (eV)=1242/λ_(max)  Conversion Equation 2

In order to measure HOMO energy level, each of the compounds wasdeposited on a glass substrate with a thickness of 50 nm and then eachsample was subject to photoelectron spectroscopy (Riken Keiki, AC-2).LUMO energy level was calculated from the following Conversion Equation3:LUMO energy level (eV)=|HOMO−S ₁|  Conversion Equation 3

The evaluation results are indicted in Table 1. Energy levels of mCBP,which was used as a host in an emitting material layer, were included inTable 1 based upon literature values.

TABLE 1 Energy Level of Compound Compound S₁(eV) T₁(eV) HOMO (eV) LUMO(eV) Eg (eV) mCBP 3.60 2.90 −6.00 −2.40 3.60 A-1 2.91 2.69 −5.77 −2.862.91 A-2 2.80 2.65 −5.50 −2.70 2.80 B-1 2.64 2.50 −5.50 −2.86 2.64 Eg:LUMO − HOMO

Example 1: Fabrication of Organic Light Emitting Diode (OLED)

An organic light emitting diode was fabricated applying CBP as a host,Compound A-1 as a first delayed fluorescent dopant and Compound B-1 as asecond delayed fluorescent dopant into an emitting material layer. TheITO substrate was washed by UV-Ozone treatment before using it, and wastransferred to a vacuum chamber for depositing emission layer.Subsequently, an anode, an emission layer and a cathode were depositedby evaporation from a heating boat under 10⁻⁷ Torr vacuum condition asthe following order:

An anode (ITO, 500 Å); a hole injection layer (HIL) (HAT-CN; 70 Å); ahole transport layer (HTL) (NPB, 500 Å); an electron blocking layer(EBL) (3Cz; 100 Å); an emitting material layer (EML)(mCBP:A-1:B-1=79:20:1 by weight ratio; 250 Å); a hole blocking layer(HBL) (TSPO1; 150 Å); an electron transport layer (ETL) (TPBi; 350 Å);an electron injection layer (EIL) (LiF; 10 Å); and a cathode (Al; 1000Å).

And then, capping layer (CPL) was deposited over the cathode and thedevice was encapsulated by glass. After deposition of emissive layer andthe cathode, the OLED was transferred from the deposition chamber to adry box for film formation, followed by encapsulation using UV-curableepoxy resin and moisture getter. The manufacture organic light emittingdiode had an emission area of 9 mm². The energy levels among the host(H), the first delayed fluorescent dopant (TD1) and the second delayedfluorescent dopant (TD2) are as follows: HOMO^(H)−HOMO^(TD1)=−0.23 eV;HOMO^(TD2)−HOMO^(TD1)=0.27 eV; LUMO^(H)−LUMO^(TD1)=0.46 eV;LUMO^(TD1)=LUMO^(TD2).

Example 2: Fabrication of OLED

An OLED was fabricated using the same materials as Example 1, exceptthat an EML having a double-layered structure, i.e. a second emittingmaterial layer of host and second delayed fluorescent dopant (mCBP:B-1=80:20 by weight ratio; 100 Å) on the EBL and a first emittingmaterial layer of host and first delayed fluorescent dopant (mCBP:A-1=80:20 by weight ratio, 150 Å), has been laminated instead of thesingle-layered EML. The energy levels among the host (H), the firstdelayed fluorescent dopant (TD1) and the second delayed fluoresecentdopant (TD2) are the same as in Example 1.

Comparative Example 1: Fabrication of OLED

An OLED was fabricated using the same materials as Example 1, exceptthat luminous materials mCBP (host): A-1 (delayed fluorescent dopant)(80:20 by weight ratio; Ref 1) have been used in the EML instead ofmCBP: A-1: B-1. The energy levels among the host (H) and the delayedfluorescent dopant (TD) are as follows: HOMO^(H)−HOMO^(TD)=−0.23 eV;LUMO^(H)−LUMO^(TD)=0.46 eV.

Comparative Example 2: Fabrication of OLED

An OLED was fabricated using the same materials as Example 1, exceptthat luminous materials mCBP (host): B-1 (delayed fluorescent dopant)(80:20 by weight ratio; Ref 2) have been used in the EML instead ofmCBP: A-1: B-1. The energy levels among the host (H) and the delayedfluorescent dopant (TD) are as follows: HOMO^(H)−HOMO^(TD)=−0.50 eV;LUMO^(H)−LUMO^(TD)=0.46 eV.

Comparative Example 3: Fabrication of OLED

An OLED was fabricated using the same materials as Example 1, exceptthat luminous materials mCBP (host): A-2 (delayed fluorescent dopant)(80:20 by weight ratio; Ref. 3) have been used in the EML instead ofmCBP: A-1: B-1. The energy levels among the host (H) and the delayedfluorescent dopant (TD) are as follows: HOMO^(H)−HOMO^(TD)=−0.50 eV;LUMO^(H)−LUMO^(TD)=0.30 eV.

Comparative Example 4: Fabrication of OLED

An OLED was fabricated using the same materials as Example 1, exceptthat luminous materials mCBP (host): A-2 (first delayed fluorescentdopant): B-1 (second delayed fluorescent dopant) (79:20:1 by weightratio, Ref. 4) have been used in the EML instead of mCBP: A-1: B-1. Theenergy levels among the host (H), the first delayed fluorescent dopant(TD1) and the second delayed fluorescent dopant (TD2) are as follows:HOMO^(H)−HOMO^(TD1)=−0.50 eV; HOMO^(TD2)=HOMO^(TD1);LUMO^(H)−LUMO^(TD1)=0.30 eV; LUMO^(TD1)−LUMO^(TD2)=0.16 eV.

Comparative Example 5: Fabrication of OLED

An OLED was fabricated using the same materials as Example 1, exceptthat luminous materials, mCBP (host): A-2 (delayed fluorescent dopant):fluorescent dopant as indicated below (79:20:1 by weight ratio; Ref 5)have been used in the EML instead of mCBP: A-1: B-1. The energy levelsamong the host (H) and the delayed fluorescent dopant are as follows:HOMO^(H)−HOMO^(TD)=−0.50 eV; LUMO^(H)−LUMO^(TD)=0.30 eV.

Fluorescent Dopant

Comparative Example 6: Fabrication of OLED

An OLED was fabricated using the same materials as Example 2, exceptthat luminous materials mCBP (host): the fluorescent dopant (seconddopant) (80:20 by weight ratio; 100 Å) in the second EML (Ref. 6) havebeen used instead of mCBP: B-1. The energy levels among the host (H) andthe delayed fluorescent dopant (A-1; TD) are as follows:HOMO^(H)−HOMO^(TD)=−0.23 eV; LUMO^(H)−LUMO^(TD)=0.46 eV.

Experimental Example 2: Measurement of Luminous Properties of OLED

Each of the organic light emitting diode fabricated by Examples 1 to 2and Comparative Examples 1 to 6 was connected to an external powersource, and luminous properties for all the diodes were evaluated usinga constant current source (KEITHLEY) and a photometer PR650 at roomtemperature. In particular, maximum External Quantum Efficiency(EQE_(max); %), External Quantum Efficiency (EQE, %), maximumElectroluminescence Wavelength (λ_(max); nm), FWHM (nm) and CIE colorcoordinates (CIE_(x), CIE_(y)) at a current density of 10 mA/cm² of thelight emitting diodes of Examples 1 to 2 and Comparative Examples 1 to 6(Ref. 1-6) were measured. The results thereof are shown in the followingTable 2 and in FIGS. 12 to 14.

TABLE 2 Luminous Properties of OLED EQE_(max) EQE λ_(max) FWHM Sample(%) (%) (nm) (nm) CIE_(x) CIE_(y) Ref. 1 8.0 4.9 466 65 0.148 0.192 Ref.2 10 4.2 464 33 0.132 0.133 Ref. 3 9.2 6.4 473 71 0.150 0.241 Ref. 4 9.67.2 464 36 0.141 0.152 Ref. 5 4.5 4.0 462 51 0.143 0.160 Ref. 6 4.0 3.8463 53 0.145 0.165 Example 1 18.2 11.0 462 35 0.139 0.145 Example 2 16.28.2 464 40 0.142 0.165

As indicated in Table 2 and FIGS. 12-14, each of the organic lightemitting diodes of Examples 1 to 2 including two delayed fluorescentdopants whose energy levels are controlled in the EML had an enhancedluminous efficiency and color purity owing to narrow FWHM.

Particularly, compared with the OLEDs only using the second delayedfluorescent dopant in Comparative Example 2, the OLED using twodifferent delayed fluorescent dopants whose energy levels are controlled(Example 1) hand a maximum EQE which is improved by 82% and an EQE whichis improved by 162.0% (See, FIG. 12). Compared with the OLEDs which areonly using the first delayed fluorescent dopants “A-1” and “A-2”(Comparative Examples 1 and 3), the OLED in Example 1 had an improvedcolor purity owing to its narrow FWHM and can implement deep blue coloras indicated in the CIE color coordinates.

In addition, compared with the OLED which includes different delayedfluorescent dopants whose HOMO energy levels are identical (ComparativeExample 4), the OLED in Example 1 has a maximum EQE which is enhanced by89.6% and an EQE which is enhanced by 52.8%. Compared with the OLED onlyusing the first delayed fluorescent dopant (Comparative Example 3), theOLED applying the second delayed fluorescent dopant whose energy levelsare not controlled (Comparative Example 4) did not show an improvedluminous efficiency (See, FIG. 13).

Moreover, compared with the OLED applying the fluorescent dopant insteadof the second delayed fluorescent dopant in Comparative Example 5, theOLED in Example 1 has a maximum EQE which is improved by 304.4% and anEQE which is improved by 175% (See, FIG. 14). In addition, the OLED inExamples 1 and 2 have an improved color purity due to their narrow FWHMcompared with the OLEDs using the fluorescent dopant in ComparativeExamples 5 and 6. Particularly, compared with the OLED using thefluorescent dopant as the final luminous material (Comparative Example5), the OLED using the delayed fluorescent dopant whose energy levelsare controlled has an enhanced color purity as well as an enhancedluminous efficiency. Compared with the OLED using the fluorescent dopantwithin one EML among two EMLs in Comparative Example 6, the OLEDapplying two different delayed fluorescent dopants whose energy levelsare controlled into each of two EMLs in Example 2 has a maximum EQEwhich is improved by 305% and an EQE which is improved by 115.8%, aswell as an improved color purity.

While the present disclosure has been described with reference toexemplary embodiments and examples, these embodiments and examples arenot intended to limit the scope of the present disclosure. Rather, itwill be apparent to those skilled in the art that various modificationsand variations can be made in the present disclosure without departingfrom the spirit or scope of the invention. Thus, it is intended that thepresent disclosure covers the modifications and variations of thepresent disclosure provided they come within the scope of the appendedclaims and their equivalents.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. An organic light emitting diode,comprising: a first electrode; a second electrode, wherein the first andsecond electrodes face each other; and at least one emitting unitdisposed between the first and second electrodes, wherein the at leastone emitting unit comprises an emitting material layer, wherein theemitting material layer comprises a first host, a first delayedfluorescent dopant and a second delayed fluorescent dopant, wherein eachof an excited state singlet energy level (S₁ ^(TD1)) and an excitedstate triplet energy level (T₁ ^(TD1)) of the first delayed fluorescentdopant is higher than each of an excited state singlet energy level (S₁^(TD2)) and an excited state triplet energy level (T₁ ^(TD2)) of thesecond delayed fluorescent dopant, respectively, wherein a highestoccupied molecular orbital (HOMO) energy level (HOMO^(H)) of the firsthost, a HOMO energy level (HOMO^(TD1)) of the first delayed fluorescentdopant and a HOMO energy level (HOMO^(TD2)) of the second delayedfluorescent dopant satisfy the following relationships in Equations (1)and (3), and wherein a lowest unoccupied molecular orbital (LUMO) energylevel (LUMO^(H)) of the first host, a LUMO energy level (LUMO^(TD1)) ofthe first delayed fluorescent dopant and a LUMO energy level(LUMO^(TD2)) of the second delayed fluorescent dopant satisfy thefollowing relationships in Equations (5) and (7)HOMO^(H)≤HOMO^(TD1)  (1)HOMO^(TD2)−HOMO^(TD1)>0.2 eV  (3)LUMO^(H)>LUMO^(TD1)  (5)LUMO^(TD1)≥LUMO^(TD2)  (7).
 2. The organic light emitting diode of claim1, wherein the HOMO energy level (HOMO^(H)) of the first host, the HOMOenergy level (HOMO^(TD1)) of the first delayed fluorescent dopant andthe HOMO energy level (HOMO^(TD2)) of the second delayed fluorescentdopant satisfy the following relationships in Equations (2) and (4)|HOMO^(H)−HOMO^(TD1)|<0.3 eV  (2)0.2 eV<HOMO^(TD2)−HOMO^(TD1)<1.0 eV  (4).
 3. The organic light emittingdiode of claim 1, wherein the LUMO energy level (LUMO^(H)) of the firsthost, the LUMO energy level (LUMO^(TD1)) of the first delayedfluorescent dopant and the LUMO energy level (LUMO^(TD2)) of the seconddelayed fluorescent dopant satisfy the following relationships inEquations (6) and (8)0.3 eV<LUMO^(H)−LUMO^(TD1)<1.0 eV  (6)|LUMO^(TD1)−LUMO^(TD2)<0.2 eV  (8).
 4. The organic light emitting diodeof claim 1, wherein the first delayed fluorescent dopant includes anorganic compound having the following structure of Chemical Formula 1:

wherein each of R₁ and R₂ is independently a C₅˜C₃₀ aryl group or aC₄˜C₃₀ hetero aryl group; R₃ is halogen, a C₁˜C₂₀ alkyl halide, a cyanogroup, a nitro group, a linear or branched C₁˜C₂₀ alkyl group, a C₁˜C₂₀alkoxy group, a C₅˜C₃₀ aryl group unsubstituted or substituted with agroup selected from halogen, a C₁˜C₂₀ alkyl halide, a cyano group, anitro group and combinations thereof, or a C₄˜C₃₀ hetero aryl groupunsubstituted or substituted with a group selected from halogen, aC₁˜C₂₀ alkyl halide, a cyano group, a nitro group and combinationsthereof; m is a number of substituent and is an integer of 1 to 5; Ar₁is a C₁₀˜C₃₀ fused hetero aryl group; and L is a C₅˜C₃₀ arylene groupunsubstituted or substituted with one or more groups selected fromhalogen, a C₁˜C₂₀ alkyl halide, a cyano group, a nitro group andcombinations thereof, or a C₄˜C₃₀ hetero arylene group unsubstituted orsubstituted with one or more selected from halogen, a C₁˜C₂₀ alkylhalide, a cyano group, a nitro group and combinations thereof.
 5. Theorganic light emitting diode of claim 1, wherein the first delayedfluorescent dopant includes an organic compound having the followingstructure of Chemical Formula 2:

wherein each of R₁₁ and R₁₂ is independently a C₅˜C₂₀ aryl group; andeach of R₁₃ to R₂₀ is independently protium, deuterium, tritium, a cyanogroup, a linear or branched C₁˜C₁₀ alkyl group, a C₅˜C₃₀ aryl aminogroup unsubstituted or substituted with C₅˜C₂₀ aryl group, a C₅˜C₃₀ arylgroup unsubstituted or substituted with a cyano group, or a C₄˜C₃₀hetero aryl group unsubstituted or substituted with a cyano group. 6.The organic light emitting diode of claim 1, wherein the first delayedfluorescent dopant includes anyone having the following structure ofChemical Formula 3:


7. The organic light emitting diode of claim 1, wherein the seconddelayed fluorescent dopant includes an organic compound having thefollowing structure of Chemical Formula 4:

wherein each of R₃₁ and R₃₂ is independently a linear or branched C₁˜C₂₀alkyl group, a C₁˜C₂₀ alkoxy group, a C₅˜C₃₀ aryl group, a C₄˜C₃₀ heteroaryl group or an aromatic or hetero aromatic amino group, wherein theamino group is substituted with a group selected from the groupconsisting of a C₅˜C₃₀ aryl group, a C₄˜C₃₀ hetero aryl group, a C₅˜C₃₀aryl amino group unsubstituted or substituted with a C₅˜C₂₀ aryl group,a C₄˜C₃₀ hetero aryl amino group unsubstituted or substituted with aC₄˜C₂₀ hetero aryl group and combinations thereof, or two adjacentgroups among each of R₃₁ and R₃₂ form respectively a C₅˜C₂₀ fusedaromatic ring or a C₄˜C₂₀ fused hetero aromatic ring, wherein each ofthe C₅˜C₂₀ fused aromatic ring and the C₄˜C₂₀ fused hetero aromatic ringis independently unsubstituted or substituted with a C₅˜C₂₀ aryl groupor a C₄˜C₂₀ hetero aryl group; each of and p is a number of asubstituent and an integer of 0 to 3; each of R₃₃ and R₃₄ isindependently protium, deuterium, tritium, a linear or branched C₁˜C₂₀alkyl group, a C₁˜C₂₀ alkoxy group, a C₅˜C₃₀ aryl group or a C₄˜C₃₀hetero aryl group; R₃₅ is protium, deuterium, tritium, linear orbranched a C₁˜C₂₀ alkyl group, a C₁˜C₂₀ alkoxy group or an aromatic orhetero aromatic amino group, wherein the amino group is substituted witha group selected from the group consisting of a C₅˜C₃₀ aryl group, aC₄˜C₃₀ hetero aryl group and combinations thereof.
 8. The organic lightemitting diode of claim 1, wherein the second delayed fluorescent dopantincludes an organic compound having the following structure of ChemicalFormula 5:

wherein each of R_(41a), R_(41b), R_(42a) and R_(42b) is independentlyprotium, deuterium, tritium, a linear or branched C₁˜C₁₀ alkyl group, aC₅˜C₃₀ aryl group, a C₄˜C₃₀ hetero aryl group or an aromatic or heteroaromatic amino group, wherein the amino group is substituted with agroup selected from the group consisting of a C₅˜C₃₀ aryl group, aC₄˜C₃₀ hetero aryl group, a C₅˜C₃₀ aryl amino group unsubstituted orsubstituted with a C₅˜C₂₀ aryl group, a C₄˜C₃₀ hetero aryl amino groupunsubstituted or substituted with a C₄˜C₂₀ hetero aryl group andcombinations thereof, or two adjacent groups among R_(41a), R_(41b),R_(42a) and R_(42b) form respectively a C₄˜C₂₀ fused hetero aryl ringunsubstituted or substituted with a C₅˜C₂₀ aryl group; each of R₄₃ andR₄₄ is independently protium, deuterium, tritium, a linear or branchedC₁˜C₁₀ alkyl group or an aromatic or hetero aromatic amino group,wherein the amino group is substituted with a group selected from thegroup consisting of a C₅˜C₃₀ aryl group, a C₄˜C₃₀ hetero aryl group andcombinations thereof; R₄₅ is protium, deuterium tritium, a linear orbranched C₁˜C₂₀ alkyl group, a C₁˜C₂₀ alkoxy group or an aromatic orhetero aromatic amino group, wherein the amino group is substituted witha group selected from the group consisting of C₅˜C₃₀ aryl group, C₄˜C₃₀hetero aryl group and combinations thereof.
 9. The organic lightemitting diode of claim 1, wherein the second delayed fluorescent dopantincludes anyone having the following structure of Chemical Formula 6:


10. The organic light emitting diode of claim 1, wherein the excitedstate triple energy level (T₁ ^(TD1)) of the first delayed fluorescentdopant is lower than an excited state triplet energy level (T₁ ^(H)) ofthe first host.
 11. The organic light emitting diode of claim 1, whereinthe at least one emitting unit comprises a first emitting unit disposedbetween the first and second electrodes, comprising a lower emittingmaterial layer, and a second emitting unit disposed between the firstemitting unit and the second electrode, comprising an upper emittingmaterial layer, wherein at least one of the lower emitting materiallayer and the upper emitting material layer comprises the first host,the first delayed fluorescent dopant and the second delayed fluorescentdopant, and wherein the organic light emitting diode further comprises acharge generation layer disposed between the first and second emittingunits.
 12. The organic light emitting diode of claim 11, wherein theHOMO energy level (HOMO^(H)) of the first host, the HOMO energy level(HOMO^(TD1)) of the first delayed fluorescent dopant and the HOMO energylevel (HOMO^(TD2)) of the second delayed fluorescent dopant satisfy thefollowing relationships in Equations (2) and (4)|HOMO^(H)−HOMO^(TD1)|<0.3 eV  (2)0.2 eV<HOMO^(TD2)−HOMO^(TD1)<1.0 eV  (4).
 13. The organic light emittingdiode of claim 11, wherein the LUMO energy level (LUMO^(H)) of the firsthost, the LUMO energy level (LUMO^(TD1)) of the first delayedfluorescent dopant and the LUMO energy level (LUMO^(TD2)) of the seconddelayed fluorescent dopant satisfy the following relationships inEquations (6) and (8)0.3 eV<LUMO^(H)−LUMO^(TD1)<1.0 eV  (6)|LUMO^(TD1)−LUMO^(TD2)<0.2 eV  (8).
 14. The organic light emitting diodeof claim 11, wherein the excited state triple energy level (T₁ ^(TD1))of the first delayed fluorescent dopant is lower than an excited statetriplet energy level (T₁ ^(H)) of the first host.
 15. An organic lightemitting diode, comprising: a first electrode; a second electrode,wherein the first electrode and second electrode face each other; and atleast one emitting unit, wherein the at least one emitting unit isdisposed between the first and second electrodes and comprises anemitting material layer, wherein the emitting material layer comprises afirst emitting material layer disposed between the first and secondelectrodes, wherein the first emitting material layer comprises a firsthost and a first delayed fluorescent dopant, and a second emittingmaterial layer disposed between the first electrode and the firstemitting material layer or between the first emitting material layer andthe second electrode, wherein the second emitting material layercomprises a second host and a second delayed fluorescent dopant, whereineach of an excited state singlet energy level (S₁ ^(TD1)) and an excitedstate triplet energy level (T₁ ^(TD1)) of the first delayed fluorescentdopant is higher than each of an excited state singlet energy level (S₁^(TD2)) and an excited state triplet energy level (T₁ ^(TD2)) of thesecond delayed fluorescent dopant, respectively, wherein a highestoccupied molecular orbital (HOMO) energy level (HOMO^(H)) of the firsthost, a HOMO energy level (HOMO^(TD1)) of the first delayed fluorescentdopant and a HOMO energy level (HOMO^(TD2)) of the second delayedfluorescent dopant satisfy the following relationships in Equations (1)and (3), and wherein a lowest unoccupied molecular orbital (LUMO) energylevel (LUMO^(H)) of the first host, a LUMO energy level (LUMO^(TD1)) ofthe first delayed fluorescent dopant and a LUMO energy level(LUMO^(TD2)) of the second delayed fluorescent dopant satisfy thefollowing relationships in Equations (5) and (7)HOMO^(H)≤HOMO^(TD1)  (1)HOMO^(TD2)−HOMO^(TD1)>0.2 eV  (3)LUMO^(H)>LUMO^(TD1)  (5)LUMO^(TD1)≥LUMO^(TD2)  (7).
 16. The organic light emitting diode ofclaim 15, wherein the HOMO energy level (HOMO^(H)) of the first host,the HOMO energy level (HOMO^(TD1)) of the first delayed fluorescentdopant and the HOMO energy level (HOMO^(TD2)) of the second delayedfluorescent dopant satisfy the following relationships in Equations (2)and (4)|HOMO^(H)−HOMO^(TD1)|<0.3 eV  (2)0.2 eV<HOMO^(TD2)−HOMO^(TD1)<1.0 eV  (4).
 17. The organic light emittingdiode of claim 15, wherein the LUMO energy level (LUMO^(H)) of the firsthost, the LUMO energy level (LUMO^(TD1)) of the first delayedfluorescent dopant and the LUMO energy level (LUMO^(TD2)) of the seconddelayed fluorescent dopant satisfy the following relationships inEquations (6) and (8)0.3 eV<LUMO^(H)−LUMO^(TD1)<1.0 eV  (6)|LUMO^(TD1)−LUMO^(TD2)|<0.2 eV  (8).
 18. The organic light emittingdiode of claim 15, wherein the excited state triple energy level (T₁^(TD1)) of the first delayed fluorescent dopant is lower than an excitedstate triplet energy level (T₁H) of the first host.
 19. The organiclight emitting diode of claim 15, wherein the second emitting materiallayer is disposed between the first electrode and the first emittingmaterial layer, and the organic light emitting diode further comprisesan electron blocking layer disposed between the first electrode and thesecond emitting material layer.
 20. The organic light emitting diode ofclaim 19, wherein the second host is a same as a material of theelectron blocking layer.
 21. The organic light emitting diode of claim15, wherein the second emitting material layer is disposed between thefirst emitting material layer and the second electrode, and the organiclight emitting diode further comprises a hole blocking layer disposedbetween the second emitting material layer and the second electrode. 22.The organic light emitting diode of claim 21, wherein the second host isa same as a material of the hole blocking layer.
 23. The organic lightemitting diode of claim 15, wherein each of an excited state singletenergy level (S₁ ^(H1)) and an excited state triplet energy level (T₁^(H1)) of the first host is higher than each of the excited statesinglet energy level (S₁ ^(TD1)) and the excited state triplet energylevel (T₁ ^(TD1)) of the first delayed fluorescent dopant, respectively,and wherein each of an excited state singlet energy level (S₁ ^(H2)) andan excited state triplet energy level (T₁ ^(H2)) of the second host ishigher than each of the excited state singlet energy level (S₁ ^(TD2))and the excited state triplet energy level (T₁ ^(TD2)) of the seconddelayed fluorescent dopant, respectively.
 24. The organic light emittingdiode of claim 15, further comprising a third emitting material layerdisposed oppositely to the second emitting material layer with respectto the first emitting material layer, wherein the third emittingmaterial layer comprises a third host and a third delayed fluorescentdopant.
 25. The organic light emitting diode of claim 24, wherein thefirst emitting material layer is disposed between the first electrodeand the second emitting material layer and the third emitting materiallayer is disposed between the second emitting material layer and thesecond electrode, and the organic light emitting diode further comprisesan electron blocking layer disposed between the first electrode and thefirst emitting material layer.
 26. The organic light emitting diode ofclaim 25, wherein the first host is a same as a material of the electronblocking layer.
 27. The organic light emitting diode of claim 25,further comprising a hole blocking layer disposed between the thirdemitting material layer and the second electrode.
 28. The organic lightemitting diode of claim 27, wherein the third host is a same as amaterial of the hole blocking layer.
 29. The organic light emittingdiode of claim 24, wherein an excited state singlet energy level (S₁^(TD3)) and an excited state triplet energy level (T₁ ^(TD3)) of thethird delayed fluorescent dopant is higher than each of the excitedstate singlet energy level (S₁ ^(TD2)) and the excited state tripletenergy level (T₁ ^(TD)2) of the second delayed fluorescent dopant,respectively.
 30. The organic light emitting diode of claim 24, whereineach of an excited state singlet energy level (S₁ ^(H1)) and an excitedstate triplet energy level (T₁ ^(H1)) of the first host is higher thaneach of the excited state singlet energy level (S₁ ^(TD1)) and theexcited state triplet energy level (T₁ ^(TD1)) of the first delayedfluorescent dopant, respectively, wherein each of an excited statesinglet energy level (S₁ ^(H2)) and an excited state triplet energylevel (T₁ ^(H2)) of the second host is higher than each of the excitedstate singlet energy level (S₁ ^(TD2)) and the excited state tripletenergy level (T₁ ^(TD2)) of the second delayed fluorescent dopant,respectively, and wherein each of an excited state singlet energy level(S₁ ^(H3)) and an excited state triplet energy level (T₁ ^(H3)) of thethird host is higher than each of an excited state singlet energy level(S₁ ^(TD3)) and an excited state triplet energy level (T₁ ^(TD3)) of thesecond delayed fluorescent dopant, respectively.
 31. The organic lightemitting diode of claim 15, wherein the first delayed fluorescent dopantcomprises an organic compound having the following structure of ChemicalFormula 1:

wherein each of R₁ and R₂ is independently a C₅˜C₃₀ aryl group or aC₄˜C₃₀ hetero aryl group; R₃ is halogen, a C₁˜C₂₀ alkyl halide, a cyanogroup, a nitro group, a linear or branched C₁˜C₂₀ alkyl group, C₁˜C₂₀alkoxy group, a C₅˜C₃₀ aryl group unsubstituted or substituted with agroup selected from halogen, a C₁˜C₂₀ alkyl halide, a cyano group, anitro group and combinations thereof, or a C₄˜C₃₀ hetero aryl groupunsubstituted or substituted with a group selected from halogen, aC₁˜C₂₀ alkyl halide, a cyano group, a nitro group and combinationsthereof; m is a number of substituent and is an integer of 1 to 5; An isa C₁₀˜C₃₀ fused hetero aryl group; and L is a C₅˜C₃₀ arylene groupunsubstituted or substituted with one or more groups selected fromhalogen, a C₁˜C₂₀ alkyl halide, a cyano group, a nitro group andcombinations thereof, or a C₄˜C₃₀ hetero arylene group unsubstituted orsubstituted with one or more groups selected from halogen, a C₁˜C₂₀alkyl halide, a cyano group, a nitro group and combinations thereof. 32.The organic light emitting diode of claim 15, wherein the first delayedfluorescent dopant includes an organic compound having the followingstructure of Chemical Formula 2:

wherein each of R₁₁ and R₁₂ is independently C₅˜C₂₀ aryl group; and eachof R₁₃ to R₂₀ is independently protium, deuterium, tritium, cyano group,linear or branched C₁˜C₁₀ alkyl group, C₅˜C₃₀ aryl amino groupunsubstituted or substituted with C₅˜C₂₀ aryl group, C₅˜C₃₀ aryl groupunsubstituted or substituted with cyano group, or C₄˜C₃₀ hetero arylgroup unsubstituted or substituted with cyano group.
 33. The organiclight emitting diode of claim 15, wherein the first delayed fluorescentdopant includes anyone having the following structure of ChemicalFormula 3:


34. The organic light emitting diode of claim 15, wherein the seconddelayed fluorescent dopant includes an organic compound having thefollowing structure of Chemical Formula 4:

wherein each of R₃₁ and R₃₂ is independently a linear or branched C₁˜C₂₀alkyl group, a C₁˜C₂₀ alkoxy group, a C₅˜C₃₀ aryl group, a C₄˜C₃₀ heteroaryl group or an aromatic or hetero aromatic amino group, wherein theamino group is substituted with a group selected from the groupconsisting of a C₅˜C₃₀ aryl group, a C₄˜C₃₀ hetero aryl group, a C₅˜C₃aryl amino group unsubstituted or substituted with a C₅˜C₂₀ aryl group,a C₄˜C₃₀ hetero aryl amino group unsubstituted or substituted with aC₄˜C₂₀ hetero aryl group and combinations thereof, or two adjacentgroups among each of R₃₁ and R₃₂ form respectively a C₅˜C₂₀ fusedaromatic ring or a C₄˜C₂₀ fused hetero aromatic ring, wherein each ofthe C₅˜C₂₀ fused aromatic ring and the C₄˜C₂₀ fused hetero aromatic ringis independently unsubstituted or substituted with a C₅˜C₂₀ aryl groupor a C₄˜C₂₀ hetero aryl group; each of o and p is a number of asubstituent and an integer of 0 to 3; each of R₃₃ and R₃₄ isindependently protium, deuterium, tritium, a linear or branched a C₁˜C₂₀alkyl group, a C₁˜C₂₀ alkoxy group, a C₅˜C₃₀ aryl group or a C₄˜C₃₀hetero aryl group; R₃₅ is protium, deuterium, tritium, a linear orbranched C₁˜C₂₀ alkyl group, a C₁˜C₂₀ alkoxy group or an aromatic orhetero aromatic amino group, wherein the amino group is substituted witha group selected from the group consisting of a C₅˜C₃₀ aryl group, aC₄˜C₃₀ hetero aryl group and combinations thereof.
 35. The organic lightemitting diode of claim 15, wherein the second delayed fluorescentdopant includes an organic compound having the following structure ofChemical Formula 5:

wherein each of R_(41a), R_(41b), R₄₂ a and R_(42b) is independentlyprotium, deuterium, tritium, linear or branched C₁˜C₁₀ alkyl group,C₅˜C₃₀ aryl group, C₄˜C₃₀ hetero aryl group or aromatic or heteroaromatic amino group, wherein the amino group is substituted with agroup selected from the group consisting of C₅˜C₃₀ aryl group, C₄˜C₃₀hetero aryl group, C₅˜C₃₀ aryl amino group unsubstituted or substitutedwith C₅˜C₂₀ aryl group, C₄˜C₃₀ hetero aryl amino group unsubstituted orsubstituted with C₄˜C₂₀ hetero aryl group and combinations thereof, oradjacent two group among R_(41a), R_(41b), R_(42a) and R_(42b) formrespectively C₄˜C₂₀ fused hetero aryl ring unsubstituted or substitutedwith C₅˜C₂₀ aryl group; each of R₄₃ and R₄₄ is independently protium,deuterium, tritium, linear or branched C₁˜C₁₀ alkyl group or aromatic orhetero aromatic amino group, wherein the amino group is substituted witha group selected from the group consisting of C₅˜C₃₀ aryl group, C₄˜C₃₀hetero aryl group and combinations thereof, R₄₅ is protium, deuteriumtritium, linear or branched C₁-C₂₀ alkyl group, C₁-C₂₀ alkoxy group oraromatic or hetero aromatic amino group, wherein the amino group issubstituted with a group selected from the group consisting of C₅-C₃₀aryl group, C₄-C₃₀ hetero aryl group and combinations thereof.
 36. Theorganic light emitting diode of claim 15, wherein the second delayedfluorescent dopant includes anyone having the following structure ofChemical Formula 6:


37. The organic light emitting diode of claim 15, wherein the at leastone emitting unit includes a first emitting unit disposed between thefirst and second electrodes and including a lower emitting materiallayer, and a second emitting unit disposed between the first emittingunit and the second electrode and including an upper emitting materiallayer, wherein at least one of the lower emitting material layer and theupper emitting material layer includes the first emitting material layerand the second emitting material layer, and wherein the organic lightemitting diode further comprises a charge generation layer disposedbetween the first and second emitting units.
 38. The organic lightemitting diode of claim 37, wherein the HOMO energy level (HOMO^(H)) ofthe first host, the HOMO energy level (HOMO^(TD1)) of the first delayedfluorescent dopant and the HOMO energy level (HOMO^(TD2)) of the seconddelayed fluorescent dopant satisfy the following relationships inEquations (2) and (4)|HOMO^(H)−HOMO^(TD1)|<0.3 eV  (2)0.2 eV<HOMO^(TD2)−HOMO^(TD1)<1.0 eV  (4).
 39. The organic light emittingdiode of claim 37, wherein the LUMO energy level (LUMO^(H)) of the firsthost, the LUMO energy level (LUMO^(TD1)) of the first delayedfluorescent dopant and the LUMO energy level (LUMO^(TD2)) of the seconddelayed fluorescent dopant satisfy the following relationships inEquations (6) and (8)0.3 eV<LUMO^(H)−LUMO^(TD1)<1.0 eV  (6)|LUMO^(TD1)−LUMO^(TD2)<0.2 eV  (8)
 40. The organic light emitting diodeof claim 37, wherein the excited state triple energy level (T₁ ^(TD1))of the first delayed fluorescent dopant is lower than an excited statetriplet energy level (T₁ ^(H)) of the first host.
 41. An organic lightemitting device, comprising: a substrate; and the organic light emittingdiode according to claim 1 over the substrate.
 42. An organic lightemitting device, comprising: a substrate; and the organic light emittingdiode according to claim 15 over the substrate.